Compare PDF Files (Text & Visual)
See every changed word side by side — and every area of the page that looks different.
Original
Revised
Differences
Changes
- Deleted (original)
- Inserted (revised)
- Changed (both)
- Only in the original
- Only in the revised file
- Colour changed
| Pages | Pixels changed | Areas |
|---|
About the Compare PDF Files (Text & Visual)
Compare two versions of a PDF and see exactly what changed. The text comparison reads the words of both files and lines them up: words that were inserted, deleted or changed are highlighted on the two pages side by side and listed with their page numbers. Pages that were added or removed are found too, and text that only moved to the next page because something was inserted above it is not reported as changed.
The visual comparison draws both versions at 150 dpi and compares them pixel by pixel — for drawings, scans, stamps, signatures and layout changes that the text doesn’t show. Look at the pages side by side with the changed areas outlined, as an overlay with an onion-skin slider, or as a picture of the differences. Save a report of the changes as text or HTML. Both files stay in your browser.
How to use it
- Choose the original PDF in the first box and the revised PDF in the second — or drop both files at once (they are sorted by name). Swap exchanges them.
- Tick Ignore capital letters or Ignore punctuation if those changes don’t matter to you, and press Compare PDFs.
- Read the summary, then step through the changes with Previous change and Next change, or pick one from the list. Both pages are shown with the change highlighted.
- Choose Visual to compare how the pages look: Side by side, Overlay (move the slider to fade from one version to the other) or Differences. Check every page measures all page pairs at once.
- Press Report (TXT) or Report (HTML) to save a list of the changes.
Examples
Original: “payment within 30 days of the invoice” · Revised: “payment within 45 days of the invoice”
Changed: “30” → “45”, highlighted on page 4 of both files — 1 word changed, in 1 place
The revised file has a new page 3; everything else is the same
Page 3 of the revised file is new; the pages after it are lined up with their originals, so nothing else is reported
Two exports of a floor plan · Visual · Differences
The wall that moved is outlined: its old position in red, its new one in blue, the rest of the plan faded to gray
Common uses
- Checking what the other side changed in a contract or offer before you sign it.
- Proofreading a new edition of a report, manual or price list against the previous one.
- Finding the changes between two revisions of a drawing, where the text hardly changes.
- Making sure a re-exported, compressed or repaired PDF still looks like the original.
How the text comparison works
The text of each page is read with the exact position of every letter: the page content and the values of form fields (comments and text in hidden layers are left out). Words hyphenated at the end of a line are joined first, so a paragraph that is laid out differently still matches.
The two documents are then compared word by word, as a whole, with Myers’ difference algorithm (E. W. Myers, “An O(ND) Difference Algorithm and Its Variations”, Algorithmica 1, 1986), which finds the smallest set of insertions and deletions that turns one text into the other. A deletion right next to an insertion is shown as a change. Pages are then lined up by the words they share, so an inserted or removed page doesn’t make every later page look different.
On the pages, deleted words are red on the original, inserted words are blue on the revised file, and changed words are amber on both. If two files are so different that comparing them as a whole would take too long, their pages are lined up by the words they have in common and compared pair by pair; the summary then says so.
How the visual comparison works
Both pages are drawn at 150 dpi (lower for very large pages, to save memory), with their comments and form fields, starting from the top-left corner. A pixel counts as different only if no pixel of a similar colour lies within one pixel of it in the other version, so anti-aliasing and shifts of less than a pixel are not reported. Changed pixels close to each other are grouped into areas.
- Side by side outlines the changed areas on both pages.
- Overlay shows the revised page on top of the original; the slider fades from one to the other, so moved or resized content seems to jump.
- Differences fades both pages to light gray and paints what is only in the original red, what is only in the revised file blue, and changed colours amber.
Limitations
- Scanned pages have no text to compare. Use the Visual view, or make both files searchable first with PDF OCR.
- Changes of font, size, colour or position alone are not text changes; the Visual view shows them.
- Text that was moved elsewhere shows as deleted in one place and inserted in the other.
- Words are compared in the order the file stores them. In multi-column layouts and tables, text that is stored in a different order can show as changed.
- The visual comparison works best between versions exported from the same document. Two scans of paper are never aligned to the pixel, so they show differences everywhere.
- Comments are not compared as text; the Visual view shows them. Password-protected PDFs must be unlocked first with Unlock PDF.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
Are my files uploaded?
No. Both PDFs are opened and compared in your browser; nothing is sent to a server.
Does it find changes when pages were added or removed?
Yes. Pages are lined up by the words they share, so an inserted page is reported as new and the pages after it are still compared with their originals — in the text view and in the visual view.
Can it compare scanned PDFs?
Visually, yes, but scans of paper are never aligned to the pixel, so expect differences everywhere. To compare their words, make both files searchable first with PDF OCR, then compare the results.
What do “Ignore capital letters” and “Ignore punctuation” do?
They leave those differences out of the comparison, so “Total:” and “total” match. Punctuation means full stops, commas, quotes, dashes, brackets and the like; currency and maths symbols such as $, € and + are always compared.
Can I save the comparison?
Report (TXT) lists every change with its page numbers in a plain text file. Report (HTML) is a page you can open in any browser or print; it also includes pictures of the visual differences of the pages you checked.