Free Contract Comparison and Diff Tools Compared

A vendor sends back a contract with the message "just a few tweaks, nothing major," and no visible track changes. You need to know exactly what changed, word by word, before you sign. That is a document comparison, and you do not need paid software to run one properly. This guide (published by Adira, which sells contract review and CLM software, so we have a commercial reason to want you comparing contracts more carefully, though every tool below is free and the steps work with or without our product) tests six free ways to diff two contract versions against a real edited clause: Word's Compare, LibreOffice's Compare Document, Google Docs' Compare documents, Draftable's free online tool, Diffchecker's free Word/PDF compare, and Weave, Adira's free browser markup tool. It also covers the one thing every diff tool, free or paid, cannot do for you.

The comparison, tested with a real edited clause

We ran the same two files, a services agreement with a liability cap changed from twelve months' fees to one month's fees, through each tool below.

Tool	Word/DOCX compare	PDF compare	Detects moved text?	Detects formatting/number changes?	Offline	Free limit	Data location
Microsoft Word (Compare)	Yes, native	No, .docx only	Yes, distinct "moved" marker	Yes, as a normal tracked edit; formatting shown separately	Yes, fully local	No usage cap, but needs a licensed copy of Word	Local, files never leave your machine
LibreOffice Writer (Compare Document)	Yes, native	No dedicated PDF tool	Weak; a moved paragraph often shows as an unrelated delete-plus-insert	Yes, but merged inline with text changes	Yes, fully local	None, free forever	Local
Google Docs (Compare documents)	Yes, Docs/.docx only	No, does not support PDF	No dedicated marker; shows as delete-plus-insert	Yes for text; formatting-only differences often shown as a comment, not inline	No, requires Drive	No stated cap	Uploaded to Google Drive/servers
Draftable (free web tool)	Yes	Yes, natively, including PDF-to-Word cross-format	Yes, dedicated "moved" marker	Yes, standard word-level diff	No, browser-based	Roughly 10MB or 300 pages per file, no signup	Uploaded to Draftable's servers
Diffchecker (Word/PDF compare)	Yes	Yes	Yes, stated moved-content detection	Yes for text; also flags font, size, colour and embedded-image changes	Partial: PDF comparison runs in your browser; Word/PowerPoint files are first sent to Diffchecker's conversion service	No signup, no stated file-size cap for a one-off compare	Split by format: PDF stays client-side; Word/PPT is uploaded for conversion
Weave (Adira, free)	Not a diff tool	Not a diff tool	Not applicable	Not applicable, manual clause-by-clause markup only	Yes, fully in-browser	None, fully free	In-browser, never uploaded

Sources for the table: Microsoft's Compare Documents guide, LibreOffice's Comparing Versions of a Document help page, Google's Compare documents support page, Draftable's free comparison tool, and Diffchecker's Word/PDF compare page.

What we found running each tool

Word caught the liability cap change instantly, marking "twelve (12)" to "one (1)" as a plain red-and-blue edit, and its Reviewing Pane listed it alongside every other change as a scrollable list rather than something you have to spot visually in the document. It is the strongest free option if both files are already .docx and someone on your team has a Word licence.

LibreOffice caught the same cap change equally well, since a one-word edit inside an existing paragraph is not a moved-text case, the class of edit LibreOffice is weaker at. It is a genuinely solid, fully offline, completely free choice for .docx and .odt files; it simply has no dedicated PDF comparison tool, so a PDF needs converting to .docx first, which risks the reflow issues covered below.

Google Docs flagged the cap change as a suggested edit once both files were uploaded into Drive. Its real limitation for contract work is format: it compares Docs and Word-compatible files, not PDFs, and formatting-only differences sometimes show up as a comment rather than an inline mark, so check the comment column, not just the body text.

Draftable's free web tool is the only one here that compares a PDF against a PDF, or a PDF against a Word file, natively, without any manual conversion step, which matters because most executed contracts exist only as signed PDFs. It caught the cap change immediately and, per Draftable's own documentation, its comparison engine reports relocated text with a distinct moved marker rather than as an unrelated delete-and-insert pair. The free web version has no signup, but is capped at roughly 10MB or 300 pages per file, and both files are uploaded to Draftable's servers to run the comparison; a separate paid desktop app runs fully offline.

Diffchecker's Word/PDF compare also caught the cap change and, notably, splits its data handling by file type: comparing two PDFs runs the diff inside your browser without uploading either file, while comparing Word or PowerPoint files sends them to Diffchecker's own conversion service first, since converting those formats client-side is not practical in a browser. No signup is needed either way. This split is worth knowing before you assume "no upload" applies to every file type on the same tool.

Weave is not built to run an automated diff at all. It is a free, in-browser tool for reading a contract and marking up specific clauses, numbers, and dates as you go, with nothing ever uploaded anywhere. Used alongside a diff tool, the workflow is: run one of the five tools above for the word-by-word comparison, then use Weave to highlight and annotate the clauses the diff flagged, or the ones you are checking by hand, so your notes live on the document itself rather than in a separate email thread.

The honesty core: a diff shows changed text, not changed meaning

Every tool above passed the cap-change test because that test is exactly what a text diff is built for: spotting a character that is different between two files. That is also the limit of what any of them do. None of them read the contract. A few things a clean diff result can still be hiding:

• A redefined term. If Clause 1 redefines "Confidential Information" to drop a category it used to cover, every later clause that uses the phrase "Confidential Information" shows zero change, because the words on the page in Clause 9 did not move. The meaning of those unchanged words did.
• A moved clause with new legal effect. Content shifted from an exhibit into the operative body of the contract, or from one party's obligations section into the other's, can register as a clean "moved" marker in a good tool. The tool correctly reports what moved; it does not evaluate what moving it there now means for who is bound by it.
• A dead cross-reference. If a clause is renumbered or deleted, the diff flags that clause. It does not check whether another clause thirty pages later, which says "as set out in Clause 8", still points somewhere sensible.
• Anything outside the two files you actually compared. A contract that refers to "the pricing schedule available at [URL]" or a separate annexure sent by email is invisible to every tool in the table above, no matter how good its move detection is.

Weak tools compound this by also missing plain moved-text and swapped-number changes that a strong tool would catch outright, so choosing a capable tool from the table matters. But even the best tool in the table only tells you what characters changed. Judging whether that change is acceptable for your deal is a separate step, covered next.

The runnable test: after the diff, Ctrl+F it by hand

Do this every time, on the original files, not the diff output, and it takes under five minutes.

1. Before running any tool, write down three or four things that would hurt you most if changed: the liability cap figure, the notice period for termination, the payment due date, and the definition of any term central to the deal.
2. Run the diff and read every flagged change in the tool's list or reviewing pane, not just the ones that visually stand out on the page.
3. Separately, open both original files and Ctrl+F each of those three or four terms in both documents.
4. Read the full sentence around every hit, side by side, and confirm it still says the same thing, not just that the same words are present. A defined term can look untouched exactly where you searched while its actual definition, elsewhere in the document, has changed.

If anything does not match exactly, raise it before signature, regardless of what the automated diff reported.

Red flags when comparing versions

Normal	Red flag	Why it matters
The tool shows a clear "moved" marker for a relocated clause	The same relocated clause shows as an ordinary delete-and-insert pair	Without move detection, a relocated clause can read as deleted entirely, or you may miss that it landed somewhere with different legal effect
Every flagged change is read in the reviewing pane or change list	Only the visual redline is glanced at, the change list is never opened	A one-word edit inside a long, otherwise-unchanged paragraph is easy to skim past visually
The liability cap, key dates, and defined terms are manually Ctrl+F'd after the diff	The diff output is treated as the complete check	A diff cannot tell you that a definition elsewhere changed the meaning of text that itself never moved
A confidential contract is compared in Word, LibreOffice, or Weave	The same confidential contract is dropped into an unfamiliar "free PDF diff" website found through an ad	An unfamiliar destination may log, retain, or otherwise process an uploaded contract with no stated data terms
"No differences found" is confirmed against the correct two file names and dates	"No differences" is accepted without checking which two files were actually compared	Comparing two copies of the same file, or the wrong version pair, truthfully reports zero differences and tells you nothing about the version you actually sent
A PDF is converted to .docx and the converted text is spot-checked against the original	A PDF is converted and compared with no spot-check, on the assumption the conversion is exact	Conversion can drop or reflow text, producing differences that are artifacts of the conversion, not real edits
A tool's "detects moved text" claim is checked with a small known-edit test file first	The claim from a tool's marketing page is trusted outright on the real, high-stakes contract	Free tools vary widely in what they actually flag; a two-minute test file catches the gap before it costs you something

A version-control clause that removes the guesswork

The comparison work above exists because contracts get emailed back and forth across several drafts, and it is not always obvious which copy both sides actually mean to sign. A clause fixing that ambiguity is worth as much as any diff tool.

Bad: "The Parties agree that this Agreement, together with any amendments, represents the final agreement between them."

This says nothing about which physical file counts as "this Agreement" when several near-identical drafts have circulated by email. It gives no way to resolve a dispute about which copy is the authoritative one, and does not say a fresh signed writing is required for any later change.

Better: "This Agreement is executed in the form of the document titled '[file name], dated [date], version [X]', initialled by both Parties on its final page. In the event of any conflict between this executed document and any other draft, correspondence, or version, this executed document shall prevail. No amendment shall have effect unless made by a further instrument in writing, signed by the authorised representatives of both Parties; no change made by altering a copy of this document after execution shall have any effect."

The rewrite names the exact file, requires initials as a physical anchor to that specific version, states plainly which copy wins in a dispute, and closes off the temptation to just edit the signed file later.

Why the document itself, not your memory of the email thread, is what matters legally

Once a contract is reduced to a signed document, Indian evidence law generally will not let either side argue about the terms using anything other than that document. Section 91 of the Indian Evidence Act, 1872 (now Section 94 of the Bharatiya Sakshya Adhiniyam, 2023) puts it directly:

"When the terms of a contract... have been reduced to the form of a document... no evidence shall be given in proof of the terms of such contract... except the document itself, or secondary evidence of its contents in cases in which secondary evidence is admissible..." Source: Section 91, Indian Evidence Act, 1872

The Supreme Court explained the reasoning in Bai Hira Devi v Official Assignee of Bombay, AIR 1958 SC 448: Sections 91 and 92 rest on the "best evidence rule", the document itself is the best evidence of its own contents, not anyone's recollection of a phone call or an email exchange about what was "really" meant. Read the full judgment on Indian Kanoon. In practice, running a proper comparison before you sign is close to your only real chance to catch a change; once signed, arguing that you believed the cap was still twelve months, when the executed document says one month, is a hard argument to win.

Privacy: online diff means upload

Word's, LibreOffice's, and Weave's comparisons run entirely on your machine or in your browser; the contract never leaves your device. Google Docs, Draftable's free web tool, and (for Word/PowerPoint files specifically) Diffchecker all require uploading at least one file to run the comparison, as the table above sets out. For a routine vendor NDA that is usually a reasonable trade for the convenience. For a contract naming a salary, a bank account, or any other identifiable detail, it is worth pausing on, since that document is personal data under Indian law the moment it identifies a person, not only when it is stamped "confidential." Section 8(5) of the Digital Personal Data Protection Act, 2023 puts the underlying obligation plainly:

"A Data Fiduciary shall protect personal data in its possession or under its control, including in respect of any processing undertaken by it or on its behalf by a Data Processor, by taking reasonable security safeguards to prevent personal data breach." Source: Section 8, Digital Personal Data Protection Act, 2023 (Indian Kanoon)

Before uploading a sensitive contract to any tool, you can check what it actually sends: open your browser's developer tools (F12), go to the Network tab, and upload a throwaway test file. A large POST request firing off to the tool's domain confirms an upload is happening; almost nothing appearing in that tab is a genuine sign the tool is processing locally. If a diff output or the emails carrying both versions might ever matter later, for instance if a dispute arises over which draft was actually sent, keep them; Section 63 of the Bharatiya Sakshya Adhiniyam, 2023 (which replaced Section 65B of the Evidence Act) is the provision that governs whether an emailed draft or an electronic diff record can be produced as evidence in an Indian court, and it generally requires the record and its accompanying certificate to be kept intact, not edited after the fact.

Where this fits with the rest of your review

This page is about choosing and running a comparison tool. For the full step-by-step walkthrough of comparing two contract versions, including how each tool's interface works in detail, see how to compare two versions of a contract. If you specifically suspect the other side made changes without track changes turned on at all, a distinct and common problem, see how to catch untracked changes the other side made to your contract.

FAQ

Which free tool is best if I only have PDFs, not Word files? Draftable's free web tool and Diffchecker's Word/PDF compare both work on PDFs natively. Word requires converting a PDF to .docx first, and Google Docs does not support PDF comparison at all; LibreOffice has no dedicated PDF comparison tool either.

Is it safe to run a confidential contract through an online comparison website? Be selective. Google Docs and Draftable's free web tool both require uploading your file to run the comparison; Diffchecker uploads Word and PowerPoint files but keeps PDF-to-PDF comparisons in your browser. Word, LibreOffice, and Weave never require an upload at all. For anything under an NDA, prefer one of those three, or check the Network tab yourself before trusting an unfamiliar site.

Can any of these tools tell me whether a change is bad for me? No. Every tool in this comparison tells you what text changed. None of them judges whether that change is acceptable given your negotiating position, the stakes of the deal, or the rest of the contract. That judgment stays with you, or a lawyer, not the software.

What is the actual difference between Word's "Compare" and "Combine"? Compare shows the differences between an original and a revised copy of the same document, which is what you want when checking what a counterparty sent back. Combine merges edits from multiple reviewers working on separate copies of the same original into one document, a different job, more useful for your own team's parallel comments than for checking a returned draft.

A tool says "no differences found." Can I trust that? Only if you have checked that you compared the correct two files. If you accidentally compare two copies of the same version, or the wrong pair entirely, the tool correctly reports zero differences between those two files, which tells you nothing about what changed against the version you actually sent. Double-check file names and dates first.

Do I still need to check anything by hand if the diff comes back clean on the numbers I care about? Yes, at least once. A clean diff on the liability cap sentence itself does not rule out a changed definition elsewhere (what counts as "Fees", for instance) that quietly alters what that same, unchanged number now means.

This guide gets you to a reliable way of seeing exactly what changed between two versions of a contract, and the checks worth running by hand afterward. It does not tell you whether a specific change is acceptable for your deal, whether a version-control clause needs adapting for your situation, or whether a change you have found is enforceable against you if it slips through. Those depend on your specific facts and are not legal advice; for anything touching liability, indemnity, or termination, get a lawyer to look at the actual clause before you sign.