How to Compare Two PDF Files
To compare two PDF files, pull the text out of both and line them up word by word. PDFDEN's free PDF compare tool does that in your browser and marks additions in green and deletions in red. It also counts the changes, so you know at a glance how much moved.
Compare PDF: Spot text differences between two PDFs. Free, and your file never leaves your device.
Open Compare PDFSteps
Open Compare PDF.
Drop the older version into the first slot and the newer version into the second.
Run the comparison. The text of both files is extracted and compared locally.
Read the diff: green words were added, red words were removed. The change count sits on top.
What the comparison checks, and what it does not
The PDF diff tool compares text only. It catches changed words, numbers, dates and clauses, which is what matters in most contract and report revisions.
It does not compare images, layout, fonts or colors. Two files with identical wording but a new logo will show no differences. For visual checks, flip between the two files page by page, or render both to images with PDF to PNG and compare those side by side.
Put the older file in the first slot. The original version on the left and the revised one on the right is the usual convention. Additions and deletions are shown from the first file to the second, so swapping them swaps green and red.
How to compare scanned PDFs
A scanned PDF is a picture of a page with no text layer, so there is nothing to compare. Run each scan through OCR PDF first to add a searchable text layer, then compare the OCR'd versions.
OCR can misread a character here and there, especially on poor scans, and those show up as small differences. The guide on how to make a scanned PDF searchable has tips for cleaner results.
Compare PDF: Spot text differences between two PDFs. Free, and your file never leaves your device.
Open Compare PDFCompare PDF documents without Acrobat
Document comparison is a paid feature in most desktop PDF editors, and neither Mac Preview nor Windows has one built in.
A manual fallback: export both files to plain text with PDF to Text and compare the .txt files in any diff tool or text editor with a compare feature. The browser tool skips that step and shows the result straight away.
Keep confidential drafts private
Contract drafts are exactly the kind of file people hesitate to upload. PDFDEN extracts and compares the text inside your browser, so neither version is sent to a server.
That also means there is no account to create and nothing to delete afterward. Close the tab and both files are gone from the page. For drafts that must stay locked when you send them, add a password with Protect PDF.
How to read the comparison results
Start with the change count. A handful of changes in a long contract means a quick review. Hundreds usually mean the text was reflowed or reformatted, not rewritten.
Then scan for red and green close together. A deleted word followed by an added one is a replacement, like a changed amount, name or date. Those are the edits most worth checking.
Line breaks and page separators can shift between versions without any change in wording. If a diff looks noisy, the layout probably moved. Focus on the words themselves. The PDF comparison tool compares the text in reading order, so a paragraph that moved to another page can show as deleted in one place and added in another.