How to compare two documents and find every change
Someone sends back “a few small edits” to a contract, your colleague updates a policy, or you need to know what changed between two drafts of an essay. Reading both versions side by side is slow and unreliable: the human eye is bad at spotting a changed number or a missing “not”. A comparison tool, often called a diff tool, finds every change for you.
Option 1: Microsoft Word’s Compare feature
If both versions are Word documents, Word can compare them directly:
- Open Word and go to Review › Compare › Compare.
- Choose the original document and the revised document.
- Word creates a third document that shows every insertion and deletion as tracked changes, with a summary pane listing them.
This keeps formatting and lets you accept or reject each change. It is the best choice when you will keep working in Word.
Option 2: Google Docs
In Google Docs, open one version and choose Tools › Compare documents, then pick the other document from your Drive. Google Docs creates a new document with the differences shown as suggestions. For a single document that several people edit, File › Version history shows what changed between saved versions.
Option 3: a text diff checker
When the text comes from different places, such as a PDF, an email, a web page or code, paste both versions into a text comparison tool. Wordformat’s Diff checker compares them in your browser, so confidential documents aren’t uploaded anywhere. It works with any text you can copy, and it’s the quickest option for short passages.
How to read a diff
Diff tools compare line by line first, then show changes within lines:
- Removed text is usually shown in red on the left (the original).
- Added text is shown in green on the right (the new version).
- A line that was edited appears as both: the old line in red and the new one in green, with the exact changed words highlighted more strongly.
- Unchanged lines are shown plainly, and long stretches of them may be folded away so you can focus on the changes.
A split view shows the versions side by side, which is easiest on a wide screen. A unified view puts everything in one column with − and + markers, the format programmers know from code reviews and Git.
Tips for accurate comparisons
- Clean the text first. Text copied from a PDF often has line breaks in different places in each version, which makes every line look changed. Run both versions through Remove line breaks before comparing.
- Ignore what doesn’t matter. Options such as “Ignore extra spaces” and “Ignore upper/lower case” hide differences you don’t care about, so real changes stand out.
- Use character-level highlighting for numbers. In contracts and invoices, a single changed digit (30 days becoming 60 days) is easy to miss at word level.
- Watch for moved text. Most diff tools show a moved paragraph as a deletion in one place and an insertion in another. If you see the same text in red and green, it was probably moved, not changed.
- Check the whole document. Compare the full text rather than the section you were told changed.
Comparing images and screenshots
The same idea works for pictures. Wordformat’s Image compare tool can place two images side by side, overlay them with a slider, or highlight every pixel that changed, which is useful for checking design revisions or website screenshots before and after an update.
Is it safe to paste confidential text into an online diff tool?
It depends on the tool. Many online comparison sites send your text to their servers, and some store it to create shareable links. For contracts, medical or financial information, use a tool that works locally (Word’s Compare, or a browser-based checker like Wordformat’s, which never uploads your text), or check the site’s privacy policy first.