Compare PDFs
Compare two versions of a PDF side by side in your browser. Removed and added words are boxed on each page. Text-based PDFs only; nothing is uploaded.
Upload Original PDF
Upload Modified PDF
About This Tool
Compare PDFs places two versions of a document side by side and boxes the words that differ: removed words on the original, added words on the revised copy. It compares the text layer only. Its font check is currently unreliable and flags almost every word, so switch off the Font & Format Changes filter before you review.
Each file is read as soon as you add it: every page is drawn as an image for display, and its text is extracted with word positions. When you start the comparison, pages are first paired by how much text they share, so an inserted page appears as an inserted page instead of pushing every later pair out of step. Within each pair, a word-by-word comparison marks removals in red and additions in green. Where a removed passage of five or more characters closely matches an added one, both are marked in purple as a possible move. Hover over a box to read the words it covers.
Filters above the pages switch groups of boxes on and off: Text Changes, Font & Format Changes, Headers & Footers and Shifted Paragraphs. Changes in the top and bottom 12% of a page count as headers and footers and are hidden by default. The two panes scroll together, and a full-screen button gives more room.
Pictures, colours, lines and other non-text content are not compared. A scanned page without a text layer has no words to compare, so two different scans can look identical; run them through OCR PDF first. There is no overlay view and no report or annotated PDF to download. For a document under change control, use the boxes to find the edits, then confirm each one by reading.
Both files are processed in your browser tab and are not uploaded.
How to Use
Add the original
Drop the earlier version on the Original PDF (Left Version) box, or click it to browse. Its pages are read straight away.
Add the revised copy
Put the later version in the Modified PDF (Right Version) box. Use Remove on either card to swap a file.
Run the comparison
Click Run Semantic Comparison, then switch off the Font & Format Changes filter so that only added and removed words stay boxed.
Work through the page pairs
Use Next Page Pair and Prev Page Pair, hover over boxes to read the affected words, and click Reset Comparison to start again.
Use Cases
Check a revised SOP
Find the wording that changed between the approved procedure and the draft revision before the review meeting.
Review a returned draft
See which words a colleague or counterparty altered in a document they sent back, then read those passages closely.
Spot inserted or dropped pages
Page pairing shows a page that exists in only one version as inserted or deleted, which is easy to miss in a long file.
Frequently Asked Questions
Why is nearly every word highlighted?
The formatting check compares the internal font names that the PDF library assigns, and those names include an identifier that differs between the two files. Unchanged words are therefore marked as font changes. Switch off the Font & Format Changes filter and only real additions and removals stay boxed.
Can I compare scanned PDFs?
Only after OCR. The tool compares the text layer, and a scan without one has no words to compare, so different scans can look identical. Run both files through OCR PDF first, and expect OCR misreadings to appear as changes.
Is there an overlay view or a downloadable report?
No. Results are shown side by side on screen only, with no overlay mode, export or annotated PDF. Note the page numbers or take screenshots if you need a record of the differences.
Does it detect changes to images, tables or layout?
No. Only words are compared, so a replaced picture, a new colour or a moved table border is not flagged. Words that only change position on the page are not flagged either, unless a passage disappears in one place and appears in another, which may be marked as shifted.
How are the pages matched?
Pages are paired by how many of the same characters they contain. A page with no reasonable match in the other file is shown as inserted or deleted. The matching is approximate, so check the page numbers above each pane when a pairing looks wrong.
Are my files uploaded?
No. Both PDFs are read and compared in your browser tab, and nothing is sent to a server.