How to Mark Up a PDF Contract in the Browser (Free, No Upload)

If someone has emailed you a contract as a PDF and you need to flag three clauses before your next call, you do not need Adobe Acrobat Pro and you do not need to upload the file to a random "free PDF editor" website. Every major browser can now highlight and comment on a PDF natively, every free PDF reader worth using can add strikethrough and sticky notes, and Weave, Adira's free browser-based contract tool, does the same without an account or an upload. (Adira, which publishes this guide, sells contract review and CLM software; nothing below requires it, and the steps work the same whether you ever try Adira or not.)

This guide covers three free ways to highlight, comment on, and strike through a PDF contract: your browser's built-in viewer, a free desktop reader, and Weave. It also covers something most "annotate a PDF" guides skip: marking up a PDF is not the same as changing it, and knowing which one you actually need matters before you spend twenty minutes highlighting the wrong document.

Annotation is not redlining, and the difference is not cosmetic

A PDF annotation, a highlight, a sticky note, a strikethrough line, sits on top of the document as a separate layer. It does not touch the underlying text. If you strike through a sentence in clause 6.2 and export the file, clause 6.2 still legally says exactly what it said before. Your strikethrough is a visible request, not an edit. The other side has to open the file, see your marks, and manually retype the change into their own draft, or accept it and send back a version where the text itself has actually changed.

Redlining is the second thing: tracked changes to the actual words, done in an editable format (usually Word, sometimes a PDF that supports true text edits), where accepting a change actually alters the clause. If you need the other side to see exactly what changed and be able to accept or reject it with one click, you want tracked changes, not PDF annotation; see How to Redline a Contract for that workflow.

This distinction is not just a tooling detail. It maps onto how a contract actually gets modified under Indian law. Section 2(a) of the Indian Contract Act, 1872 defines a proposal:

"When one person signifies to another his willingness to do or to abstain from doing anything, with a view to obtaining the assent of that other to such act or abstinence, he is said to make a proposal."

And Section 2(b) defines acceptance:

"When the person to whom the proposal is made signifies his assent thereto, the proposal is said to be accepted." Source: Section 2, The Indian Contract Act, 1872 (Indian Kanoon)

A highlight or a comment on a PDF is, at best, a proposal under Section 2(a): you are signifying something to the other party, with a view to getting their assent. It is not itself an acceptance, and it is certainly not a variation of the contract. Nothing changes until the other side signifies assent, in writing, usually by sending back a version where the actual clause text is different. So marking up a PDF is a communication tool for getting to that agreement, not a substitute for it. Full guidance on doing the annotation itself, rather than the redlining, is at How to Annotate a Contract.

Method 1: your browser, no install, no upload

Both Chrome and Firefox now ship built-in PDF annotation tools, so for a quick highlight-and-comment pass you often do not need to open anything else.

In Chrome: open the PDF (drag it into a tab), click the pencil icon in the toolbar, and you get two tools: Highlight, which colours over selected text, and Note, which drops a comment pin anywhere on the page. Click an existing highlight to change its colour. There is no native strikethrough tool in Chrome's viewer as of this writing, so use Method 2 below if you need to visibly cross out a sentence.

In Firefox: open the PDF and use the toolbar at the top of the document. Select text and a highlight icon appears below the selection; there is also a freehand highlight tool, a draw (ink) tool for circling or underlining by hand, and a text tool for adding a comment box directly on the page. Firefox's engine (PDF.js) writes these as standard PDF annotation objects, so they open correctly later in Acrobat, Preview, or any other reader, not just Firefox.

Both are genuinely local: the file stays in your browser's memory and is never sent anywhere, which matters for a confidential draft. Save the file (Ctrl+S or the download icon) when you are done, and the annotations are saved inside the PDF itself.

Method 2: a free desktop reader, when you need strikethrough or a fuller toolkit

Browser-native tools cover highlight and comment well but are thin on strikethrough and layout options. For a full free toolkit:

Adobe Acrobat Reader (free, not Pro) includes strikethrough as a genuinely free feature, not a paywalled one. Go to Comment, then choose the Highlight Text tool, the Strikethrough Text tool, or the Underline Text tool from the toolbar, then drag across the text you want marked. Double-click any markup to attach a pop-up note explaining why. This is the closest free equivalent to what a lawyer marking up a contract in Acrobat Pro would do, minus the paid features (redaction, OCR, and true text editing).

Other free desktop readers: Xodo and PDF-XChange Editor (Windows) both ship highlight, strikeout, underline, and sticky-note comments free, with a lighter interface than Acrobat. On a Mac, Preview, built into macOS at no cost, has a Markup toolbar with highlight, strikethrough, and text annotation, so most Mac users never need to install anything separate.

All of these process the file on your machine, no internet connection required, though Acrobat Reader will periodically prompt you to sign in or save to its cloud, a prompt you can decline.

Method 3: Weave, when you do not want to install anything at all

If you do not want to install a reader, or you are on a machine where you cannot install software (a shared office laptop, for instance), you can mark up the contract directly in your browser using Weave, Adira's free, no-login contract tool. Open the PDF in Weave, work through it clause by clause, and highlight, comment, and flag the sections you want to raise, without creating an account or handing the file to a third-party conversion service.

Privacy: where the file actually goes matters

This is the part most "annotate a PDF free" guides skip, and it matters most for a contract, not a random document. Search "highlight PDF online" and most top results are web tools that work by uploading your file to their server, processing it there, and letting you download the result. For a public form, that is a non-issue. For a confidential vendor agreement, an employment contract with a salary figure in it, or an unannounced NDA, uploading it to an unfamiliar server is a real exposure: you do not know the retention period, whether it trains anything, or who else at that company can see it.

The browser-native tools, a locally installed desktop reader, and Weave's in-browser workflow all avoid this specific risk, because the file is processed on your device or within your own browser session, not shipped to a stranger's server first. If a contract carries another person's personal data, salary, address, ID numbers, that also puts it within scope of India's Digital Personal Data Protection Act, 2023, one more reason not to route a confidential contract through a random online converter. When in doubt, check whether a tool states it processes files locally or in-browser; if a "free" tool does not say, assume it uploads.

One separate legal point, once the file is exported: an annotated PDF is still just as valid an electronic record as the original. Section 4 of the Information Technology Act, 2000 gives electronic records the same standing as paper wherever a law requires something "in writing":

"Where any law provides that information or any other matter shall be in writing or in the typewritten or printed form, then, notwithstanding anything contained in such law, such requirement shall be deemed to have been satisfied if such information or matter is (a) rendered or made available in an electronic form; and (b) accessible so as to be usable for a subsequent reference." Source: Section 4, Information Technology Act, 2000 (Indian Kanoon)

So the file format is never the issue; the only real question is whether your comments actually persisted after saving, which is the next section.

The runnable test: export, close, and reopen

Annotations that look saved on screen sometimes are not, especially with a tool that "flattens" or "prints to PDF" instead of genuinely saving the annotation layer. Run this test every time before you send a marked-up contract onward:

1. Save or export the file (do not just leave the tab open).
2. Fully close the PDF, and if you were working in a browser tab, close the tab.
3. Reopen the saved file from scratch, ideally in a different app than the one you marked it up in (if you annotated in Firefox, reopen in Acrobat Reader or Preview).
4. Confirm every highlight, comment, and strikethrough is still visible and attached to the right sentence.

If a comment silently disappeared, the most common cause is that you used a "print to PDF" or "export flattened" option that bakes the visible marks into a flat image layer but drops the actual comment text, or one that skips the annotation layer entirely. Re-save using a plain "Save" or "Export annotated PDF" option instead, and re-run the test before you send it.

Red flags to check before you rely on a tool

Normal	Red flag	Why it matters
Tool processes the file locally or in your browser session	Tool requires you to "upload" the file to view it, no local option	Your contract sits on someone else's server, for an unknown retention period
Save/export button clearly labelled, annotations visible after reopening	Only option is "print" or "flatten," and comments vanish on reopening	You send a marked-up file that silently has no marks in it
Free tier clearly includes highlight, comment, and strikethrough	Strikethrough or comments locked behind a paywall you only discover mid-task	You waste time marking up a document in a tool that cannot do what you need
Tool works offline once the file is open	Tool refuses to open without an active internet connection	A flaky connection can interrupt work on a file you already have locally
App asks to sign in but lets you decline and still save locally	App forces cloud sign-in before it will save anything	Your file effectively gets uploaded even though you never clicked "upload"
Annotation layer opens correctly in a different PDF reader afterward	Marks only display correctly in the tool you made them in	The other side, using a different reader, may not see your marks at all

A vague comment versus a comment that actually gets acted on

Take a real limitation-of-liability clause: "Vendor's total liability under this Agreement shall not exceed the fees paid in the preceding three months."

A vague markup: highlight the sentence in yellow, add the comment "not okay." This gives the other side nothing to act on. They now have to guess whether you object to the amount, the three-month window, or the cap existing at all, and the fastest response you will get is "can you clarify?"

A markup that gets acted on: highlight the same sentence, and comment "Three months of fees is too low for a 12-month contract. We'd want this raised to twelve months of fees, or a fixed cap of at least the total contract value, whichever is higher. Happy to discuss." The comment names the specific number that is the problem and proposes a specific alternative. That is the difference between a comment that gets a redline back within a day and one that sits unanswered.

Where this fits with the rest of the review process

Marking up a PDF is one step in a longer workflow. Before you mark anything up, read the contract properly first; see How to Read and Understand a Contract for the three-pass method. Once your comments come back as a revised draft, line it up against the version you sent; see How to Compare Two Versions of a Contract. And when your comments graduate from "flag this" to "here is the exact wording I want instead," that is the point where you move from annotation to genuine redlining; see How to Redline a Contract.

US and global contrast

The tools differ less than the habits around them. In the US, PDF markup with Acrobat Reader or Mac Preview is just as common and just as free, and the annotation-versus-redlining distinction holds the same way: a comment is a request, a tracked change in an editable document is what actually gets accepted. What differs is the default format. Indian and US commercial contracts alike are usually exchanged as Word documents specifically so the other side can redline directly; PDF markup tends to be the tool for a quick flag or a one-off comment, not the primary negotiation channel on either side.

FAQ

Can I strike through text in a PDF without Adobe Acrobat Pro? Yes. The free Adobe Acrobat Reader includes a genuine Strikethrough Text tool under Comment, no Pro subscription needed. Chrome and Firefox's built-in viewers currently support highlight and comment but not a dedicated strikethrough tool.

Do my comments actually change the contract? No. A highlight, comment, or strikethrough on a PDF is a visible flag, not an edit to the underlying text. The wording only changes when the other side sends back, or you create, a version where the clause itself reads differently, which is redlining, not annotation.

Is it safe to use a free online "highlight PDF" website for a confidential contract? Be careful. Many of these sites work by uploading your file to their server to process it. For a confidential contract, prefer a tool that processes the file locally or in your browser session, your browser's built-in viewer, a desktop reader, or Weave, where the file never leaves your device.

Why did my highlights disappear when I reopened the file? Usually because you saved using a "print" or "flatten" option instead of a genuine export, which can drop the annotation layer. Run the export, close, and reopen test in this guide before sending a marked-up contract to anyone.

Will my comments show up if the other person opens the file in a different app than I used? They should, if you saved standard PDF annotations rather than a flattened image. Firefox's PDF.js and desktop readers like Acrobat Reader write standard annotation objects any compliant reader can display; test by opening the file in a second app before sending it.

Can I mark up a scanned paper contract the same way? Yes, once it is a PDF, a scanned image counts, you can highlight and comment on it the same way. If you also need to search or copy its text, it needs OCR first.

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This guide covers how to mark up a PDF contract for free and what that markup does and does not do to the contract itself. It does not tell you whether a specific clause you are flagging is actually enforceable, or how much negotiating leverage you have to get it changed; those depend on the exact wording, the relationship, and often a lawyer's judgment, not the tool you used to raise the flag.