Comparing two PDFs should not be a $20/month problem. But if you search for how to do it, the first three results are Adobe telling you to buy Acrobat. Below that are tools that let you upload two or three files before hitting a paywall or showing you a watermarked result.
There is a simpler way. This tool merges both PDFs into one file where every page shows both documents side by side. You open one file, scroll through it, and read both versions together without switching tabs or managing two windows. It runs in your browser, it is free, and your files never leave your device.
This guide covers when to use side-by-side comparison, how to do it in five steps, and how it differs from text diff tools like Draftable or Diffchecker, so you can pick the right method for your situation.
When do you actually need to compare two PDFs?
Most people end up comparing PDFs in one of these situations. If yours is on the list, you are in the right place.
Contract review before signing
You sent a contract, they sent it back. Merging both versions side by side lets you scroll through and catch any clause changes without playing a guessing game across two tabs.
Translation review
Put the original and translated document side by side on every page. Translators and clients can read both together without flipping between files.
Document version control
Compare a first draft against a final version. Useful for reports, proposals, policy documents, or any file that goes through multiple rounds of edits.
Legal document comparison
Lawyers and paralegals use side-by-side comparison to check execution versions, verify that amendments are correctly incorporated, and confirm no terms were quietly changed.
Academic and research review
Compare a paper draft against peer review comments, or put two research papers side by side to reference them while writing.
Print proofing
Publishers and designers compare a proof PDF against the approved version before sending to print, checking layout, spacing, and content in one pass.
Side-by-side vs. text diff: which one do you need?
There are two ways to compare PDFs and they solve different problems. Picking the wrong one is a common time waster.
Side-by-side comparison
Combines both PDFs into one file with pages placed next to each other. You read and review both together. Good for documents where layout and content both matter.
Best for: contract review, translations, version reading, proofing
Text diff tools
Scans both PDFs for text differences and highlights changes automatically, like track changes in Word. Does not work on scanned PDFs. Misses layout and formatting changes.
Examples: Draftable, Diffchecker, Adobe Acrobat Compare
If you are checking whether two clauses say the same thing, or reading a translation next to the original, side-by-side is what you want. If you need a computer to automatically flag every single word change in a 40-page document, a text diff tool is better. Many people use both: a quick visual review first, then a diff check on flagged sections.
How to compare two PDF documents side by side
Put the original on the left
Go to the homepage and drag your reference document into the left upload zone. For contract review this is usually the version you sent. For translation review it is the source language document.
Put the version you are checking on the right
Add the second document to the right zone. This is the one you are checking against: the returned contract, the translated document, the updated draft, or whichever version you received.
Choose Scale to fit if page sizes differ
If both documents are the same size, the default setting works. If one is A4 and the other is Letter, or one is portrait and the other landscape, pick "Scale to fit". It resizes both to the same height so neither looks stretched when placed side by side.
Download and review
Click Merge. The combined PDF downloads to your device. Open it and scroll down. Every page shows both versions next to each other in the same order. No window switching, no tab jumping.
No account needed. No watermark on the output.
Processing speed depends on your file size. Most standard documents finish in a few seconds.
Compare PDFs side by sideWhat about scanned PDFs?
This is a trap a lot of people fall into. Text diff tools fail silently on scanned PDFs because there is no actual text to compare. The tool reads pixels, not words. If you run a text diff on two scanned documents, you often get no results or completely wrong results.
Side-by-side comparison does not have this problem. Since the tool embeds whole pages as images next to each other, scanned PDFs work exactly the same as text-based ones. You get both pages on screen and you do the reading yourself.
If you need automated change detection on a scanned document, you need OCR software first to convert the scan into a text-based PDF. After that, any text diff tool will work on it.
Your files do not leave your device
Most online PDF tools send your file to a server, process it there, then delete it later. That is fine for a recipe PDF. It is not fine for a contract, an NDA, a patient record, or anything else that is actually confidential.
This tool runs entirely in your browser. When you load a file, your browser reads it locally. Nothing gets transmitted. There is no server receiving your documents. That is not a marketing claim, it is just how the browser-based JavaScript processing works.
How browser-based PDF processing keeps your files privateFrequently asked questions
Is this PDF comparison tool actually free?
Yes. No sign-up, no watermark on the output, no hidden fees. You can run as many comparisons as you want. Very large PDFs may be slow to process depending on your device, since everything runs in the browser rather than on a server.
Do my files get uploaded to a server?
No. Everything runs in your browser. Your files are read locally and never sent anywhere. This matters a lot if you are comparing contracts, legal filings, medical records, or anything else that should stay private.
What is the difference between side-by-side comparison and a text diff tool?
A text diff tool like Draftable or Diffchecker scans both PDFs for text changes and highlights them automatically. Side-by-side comparison puts both documents on the same page so you can read and spot differences yourself. Text diff is better for catching specific word changes. Side-by-side is better when you need to read and review the full content of both documents together, like comparing a translation or checking a contract layout.
Can I compare scanned PDFs?
Yes for visual comparison. Since the tool places pages side by side as images, scanned PDFs work the same as text-based ones. If you need automated text highlighting on a scanned PDF, you would first need OCR software to convert the scan to text. For reading and reviewing scanned documents together, this tool works fine.
What if the two documents have different numbers of pages?
Common when comparing an original against a revised version where pages were added or removed. The tool pairs pages by position: page 1 with page 1, page 2 with page 2, and so on. Once the shorter document ends, the remaining pages from the longer one still appear in the output, with a blank white area on the other side.
Does it work on Mac, Windows, and mobile?
Yes. It runs in the browser so the operating system does not matter. Chrome, Firefox, Safari, and Edge all work. On mobile it works too, though reviewing a side-by-side document is easier on a larger screen.
Can I compare more than two PDFs at once?
Not in a single merge. The tool combines two PDFs into one side-by-side document. If you need to compare three versions, you can run two separate merges.