File A · Original
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File B · Revised
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Comparison happens entirely in your browser's memory. Neither file is ever sent anywhere.
Added · Removed · Unchanged
Compare PDF Tool
Drop in two PDFs and see exactly what changed between them — word by word, page by page. Catch an edited answer key, a revised question paper, or a duplicated previous-year file in seconds. Nothing is ever uploaded.
Step 01 → Step 04
How the Compare PDF tool works
Spotting what's different between two versions of the same document by eye is slow and unreliable, especially across a paper that runs to several pages. This tool reads the actual text inside each PDF — the same hidden text layer that lets you select and search a PDF in any normal viewer — and lines up both files page by page to work out exactly which words were added, removed, or left untouched.
The result is a page-by-page breakdown rather than a single pass/fail verdict, so a long document with one small change in the middle doesn't get lost among dozens of otherwise identical pages.
FIG. 1 — Upload A & B → Extract & align → Compare → Review
Using the tool
A step-by-step guide
- Add File A. This is your original, baseline, or "before" version.
- Add File B. This is the revised, updated, or "after" version you want to check against File A.
- Tap "Compare PDFs." Every page is read and matched by position, then compared.
- Check the summary bar. It shows at a glance how many pages are identical, different, missing extractable text, or only present in one file.
- Review each page card. Added words appear highlighted in green, removed words in red with a strikethrough, alongside small thumbnails of both pages.
- Narrow the view if needed. Tick "Show only pages with differences" to skip past identical pages in a long document.
- Download a report if you need a record. One click saves a self-contained HTML file with every result, ready to keep, print, or share.
Decision guide
What kind of comparison do you actually need?
"Compare two PDFs" can mean a few different things depending on what you're checking for. This flowchart points to the part of the results that answers your specific question fastest.
FIG. 2 — Matching your question to the right part of the results
Under the hood
Text comparison, not a picture comparison
This tool reads each page's text content the same way a browser does when you select and copy text from a PDF, then tokenizes that text into individual words. To line two pages' wording up against each other, it runs a sequence-alignment algorithm — the same family of algorithm used by source-code diff tools like git diff — which finds the longest run of words both pages share in the same order, and treats everything outside that run as either removed from File A or added in File B.
That approach is precise about wording and indifferent to layout: two pages with identical text but different fonts, colors, margins, or images will correctly show zero word differences, because nothing about the actual words changed. For a pixel-level look at layout or formatting changes, the side-by-side thumbnails shown with every page card give you a quick visual cross-check alongside the text diff.
What this means for you
- Differences are reported at the word level, not just "this page changed," so you can see precisely what moved.
- Reordered but unchanged paragraphs may show as removed-then-added text, since the algorithm tracks sequence as well as content.
- Pages with no underlying text layer — typically scanned images — can't be word-compared and are flagged rather than guessed at.
- Very large pages get a performance safeguard that falls back to a simpler comparison rather than freezing your browser.
Privacy
Neither file ever leaves your browser
Comparing two PDFs often means handling sensitive material on both sides — an official answer key against an internal draft, or a current exam paper against a previous year's version that's supposed to stay confidential until released. That's exactly the situation where uploading either file to a third-party server is the last thing you want.
This tool keeps both files local from start to finish. Each PDF you choose is read into your browser's own memory, the text extraction and comparison run there using your device's own processing power, and the results — including the downloadable report — are generated there too. Neither file is transmitted anywhere else at any point. Closing the tab clears everything from memory, with nothing cached or logged by this tool afterward.
Built for small screens too
Comparing PDFs from a phone
Both upload areas are large, clearly labeled tap targets, and the results that follow are designed to read well in a single column on a narrow screen: thumbnails stack above their page's diff text rather than squeezing side by side into something unreadable. The "show only differences" toggle is especially useful on mobile, where scrolling past dozens of identical pages to find the two that changed is far more tedious than on a larger screen.
The downloadable comparison report opens in any mobile browser too, so a teacher checking results between classes can review, save, or forward it without needing to be back at a desktop first.
For students
Where students use Compare PDF
- Checking whether a question paper shared in a group chat matches the version officially released, to confirm it isn't an altered or fake copy.
- Comparing two drafts of personal notes after merging edits from a study partner, to see exactly what was added.
- Verifying that a "final" answer key handed out matches an earlier draft, aside from the corrections that were promised.
- Confirming two copies of a downloaded syllabus or previous-year paper are actually the same file before relying on either one.
For teachers & coaching institutes
Where staff use Compare PDF
- Confirming a sign-off answer key wasn't altered after approval, by comparing the approved version against the one actually distributed.
- Checking that a "recycled" question paper doesn't repeat a previous year's paper too closely, by comparing question text directly.
- Verifying that a revised paper only contains the intended edits, rather than accidental changes elsewhere in the document.
- Catching unauthorized edits to internal material by comparing a distributed copy against the original master file.
A necessary caveat
When this tool can't help — and what to do instead
Word-level comparison depends entirely on both PDFs having real, extractable text. A page that's actually a photograph or scan of a printed sheet, with no underlying text layer, has nothing for this tool to read, no matter how the page looks on screen. Such pages are marked clearly as having no extractable text rather than being misreported as identical or silently skipped.
When you're working with scanned material on either side, the side-by-side thumbnails shown for every page are still useful for a manual visual check, and running scanned pages through an OCR tool first — to add a real text layer — would let a future comparison work at the word level. Until then, treat any "no extractable text" page as something to check by eye rather than by automated diff.
Comparing your options
This tool versus other ways to compare two PDFs
| Approach | Cost | Privacy | Result |
|---|---|---|---|
| This browser-based tool | Free | Files never leave your device | Word-level highlights, page by page |
| Reading both files side by side manually | Free | Fully local | Slow and easy to miss small changes |
| Adobe Acrobat's Compare Files feature | Often paid or limited trial | Local, but requires installation | Detailed, including some layout-level detection |
| Server-based online diff tools | Often free with limits | Files are uploaded to a remote server | Varies in detail and accuracy |
| Comparing the original editable source files instead | Free if you still have them | Local | Most reliable, but only works pre-export |
If you still have the original editable documents that both PDFs were exported from, comparing those directly often catches more than a PDF-level comparison can, since formatting and tracked-change history are still intact. Once you only have the two finished PDFs — which is the far more common situation for question papers and answer keys passed around after the fact — a dedicated PDF comparison tool like this one is the practical option, and a browser-based one avoids both an installation step and the privacy risk of uploading potentially confidential material.
Good to know
Browser support and practical limits
This tool relies on standard browser features — reading two local files, extracting text, drawing preview thumbnails, and running a comparison algorithm — that work in current versions of Chrome, Firefox, Edge, and Safari, on both desktop and mobile.
Because everything runs on your own device, the practical limit on how large a document pair you can compare depends on your device's available memory and processing power rather than any cap built into the tool. Typical exam papers and answer keys, running from a handful of pages up to a few hundred, compare in a few seconds on most laptops and recent phones. An individual page with an unusually large amount of text triggers an automatic safeguard that switches to a lighter comparison for that page, so an extreme outlier page can't slow down or freeze the rest of the comparison.
Accessibility
Designed to be usable, not just functional
Both upload areas, the compare button, the "show only differences" toggle, and the download button are all real, labeled form elements that respond correctly to keyboard navigation and screen readers, not just mouse clicks. Added and removed words are marked with both color and a strikethrough style for removals, rather than color alone, so the distinction still reads clearly for anyone with color-vision differences.
Focus states stay clearly visible throughout, and the hero illustration's scanning-line animation is purely decorative, automatically disabled for anyone whose system has "reduce motion" turned on.
Best practice
Tips for a comparison you can trust
- Check the page-count summary first — a missing or extra page early in a document shifts every page after it, making individual page differences look bigger than they are.
- Treat "no extractable text" pages as needing a manual visual check, not as a sign the comparison failed.
- Use "Show only pages with differences" for long documents so a handful of real changes don't get buried in dozens of identical pages.
- Download the comparison report whenever the result needs to be shared or kept as a record — a screenshot loses the detail a saved report keeps.
- If wording is unchanged but the pages still look different, remember that's expected: this tool tracks words, not visual design.
Frequently asked questions
FAQ
Is this Compare PDF tool free to use?
Yes. There is no sign-up and no charge for comparing any number of PDF pairs, with no limit on how many times you use it.
Do I need to install software to compare two PDFs?
No. The comparison runs entirely inside your web browser, so there is nothing to download or install on Windows, macOS, Chromebooks, or Linux.
Are my PDFs uploaded to a server when I use this tool?
No. Both files are read and compared directly inside your browser's memory and are never sent to any server, so their contents stay private to your own device.
Why does my comparison show no differences even though the files look different?
This tool compares the actual text inside each PDF, not its visual design. If the wording is identical but fonts, colors, spacing, or images changed, the text-level comparison will correctly show no word differences even though the pages look different.
Can this tool compare scanned PDFs that don't have selectable text?
Not at the word level. A scanned page with no underlying text layer has nothing for the tool to read, so it's marked as having no extractable text, and you'll need to compare those pages visually using the side-by-side thumbnails instead.
What happens if the two files have a different number of pages?
Pages are matched by position, so page 1 is compared with page 1, and so on. Any extra pages at the end of the longer file are clearly labeled as only existing in that file, rather than being silently ignored.
Can I save or share the comparison results?
Yes. The "Download comparison report" button saves a self-contained HTML file with every page's status, word-level differences, and thumbnails, which you can open, print, or share without needing this tool again.
Does this tool work on mobile phones?
Yes. Both upload areas and the results view are sized for touch and have been built to work smoothly in mobile browsers such as Chrome on Android and Safari on iPhone.
Keep going
Related tools for exam papers and study material
Comparing two files often comes alongside other steps in the same workflow. These tools cover the rest, from organizing and labeling to merging, compressing, and archiving — each one running the same client-side way, with no file uploads.