pdfMB

Compare PDF

Put two versions of a document side by side and see every word that was added, removed or changed. Your files stay on this device.

OriginalThe older version

ChangedThe newer version

You can also choose or drop both files at once.

What to compare

Added, removed and changed words. Best for documents.

  • No uploadYour file stays on this device.
  • Your original stays as it isYou download a new copy. Your file is never changed.
  • Free, no sign-upNo account and no daily limit.

What happens to your files

Everything below happens inside your browser, on your own device. Neither PDF is uploaded, so nobody else, including us, can see them.

  1. Your browser opens both PDFs with pdf.js, the PDF viewer built into Firefox, and reads the text of every page, with the position of each word.
  2. The words of the whole document are lined up and compared in one go, not page by page. So when a paragraph grows and pushes text onto the next page, only the words that really changed are reported.
  3. Languages written without spaces, such as Thai, Chinese, Japanese and Burmese, are split into words with your browser’s built-in word breaker, so a changed word is shown as a word and not as single letters.
  4. Each change is marked at the exact place on both pages: red for what was removed from the original, green for what was added in the changed file.
  5. In Visual mode, each pair of pages is drawn as a picture at the same width and compared pixel by pixel. Areas that differ are outlined and can be shown as a red overlay.
  6. The report is a new PDF made on your device. It lists every change and shows the changed pages with their marks.
In short
  1. Choose the old and the new file
  2. Pick Text or Visual
  3. Press “Compare”
  4. Jump through the changes

How to compare two PDF files

  1. Choose the original (older) file and the changed (newer) file. If you put them the wrong way round, press “Swap”.
  2. Leave “Text” on for documents. Pick “Visual” for scans, drawings, plans or anything where the look matters more than the words.
  3. Press “Compare”. You get a summary such as “3 changes on 1 page” and a list of every change.
  4. Tap a change to jump to it. Both pages scroll together, with removed words marked in red and added words in green. On a phone, switch between the two files with the buttons above the page.
  5. Use the filters to see only added, removed or changed words. Download the PDF report or copy the list to send it to someone.

Why the whole document is compared at once

When text is added or removed, the rest of the document moves: lines wrap differently and paragraphs slide onto the next page. A page-by-page compare then reports almost everything after the edit as “changed”.

In our tests with two versions of the same research paper, comparing page by page reported 1,447 changed words. Comparing the whole document at once reported 806, because text that had only moved was no longer counted.

pdfMB therefore compares the full text from start to finish, ignores differences in spacing and line breaks, and joins words that were split with a hyphen at the end of a line.

When people use it

Contracts and agreements

Check what the other side changed in the new draft before you sign, word by word, without reading the whole contract again.

Reports and papers

See what a co-author or editor changed between two versions of a report, thesis or article.

Forms and price lists

Spot a changed number, date or name in a new version of a form, invoice or price list.

Drawings and scans

Use Visual mode to find what moved or changed in a plan, a drawing or two scans of the same page.

What it can’t do

  • Text compare only sees real text. Scans and photos of pages have none, so use Visual mode, or make them searchable with OCR first.
  • Changes in formatting, such as bold, colour or font size, are not reported by Text mode. Visual mode shows them as changed areas.
  • Text compare follows the reading order stored in the file. Tables, columns and text boxes may come out in a different order in the two files and show up as changes.
  • Visual mode compares pages with the same number, so if a page was inserted, every page after it looks different. Use Text mode for documents that changed length.
  • Two scans of the same paper never match pixel for pixel. Visual mode will mark many small areas on them.
  • Password-protected PDFs can’t be opened. Remove the password first.

Questions about comparing PDFs

Are my files uploaded?

No. pdfMB compares the two files inside your browser, and they never leave your device. You can check this in your browser’s network tools.

Can it compare Thai, Chinese or Japanese documents?

Yes. Languages without spaces between words are split into words with your browser’s word breaker, so changes are shown as whole words.

Why does it say “No differences found” when the files are different sizes?

Two PDFs can contain the same text but be saved differently, for example after compressing. Text mode compares the words, not the bytes. Use Visual mode to check the look of the pages as well.

What is the difference between Text and Visual?

Text lists the exact words that were added, removed or changed. Visual draws every page and marks the areas whose pixels differ, which also catches changes in pictures, drawings and layout.

Can I save the result?

Yes. Download the PDF report, with a summary, the full list of changes and the changed pages with their marks, or copy the list as plain text.

Is there a page or size limit?

There is no fixed limit. Long documents take longer, and very large files can run out of memory on some phones. In our tests a 142-page report was compared with itself in a few seconds on a desktop computer.