Checking two documents that are almost the same but different somewhere by eye — a report draft and its revision, or the contract you sent and the one you got back — takes a long time and is easy to get wrong. A text comparison tool finds every change mechanically. This guide sets out the steps and pitfalls of comparing documents.
This guide only explains how to carry out a comparison; it is not legal advice. Check the meaning and effect of contract terms with a professional.
Step 1: Get both documents out as text
A diff tool compares characters, not formatting. Select all the body text in the word-processor file, copy it, and paste it in. A few things to know:
- Formatting is lost. Changes to bold, underline, fonts, or colors are not compared. If you need to check formatting changes as well, also use the word processor's own compare feature (for example, Review → Compare in Microsoft Word).
- Table cells become separated by tabs or line breaks. If you copy both documents the same way, they end up in the same shape, so comparison is not affected.
- Footnotes, headers and footers, comments, and text boxes may not be included when you copy the body. Copy and compare them separately if needed.
- Automatic numbering (1., a., (i)) may be dropped or turned into plain text depending on how you copy. If clause numbers matter, make sure you extracted both sides the same way.
Step 2: Clean up text copied from PDF
PDF is a format that places characters on a page, so copying from it inserts a line break at the end of every line as it appeared on screen. If the line breaks fall in slightly different places in the two PDFs, nearly every line will show as changed. Cleaning up in this order makes the result much cleaner.
- On both sides, remove the line breaks inside paragraphs so that each paragraph becomes one line.
- Split long paragraphs into one sentence per line (a line break after each period). A change within a sentence then appears only on that line, which is easier to read.
- Delete lines that repeat on every page, such as page numbers and headers.
- If spaces were copied as several spaces, turn on Ignore amount of whitespace in the comparison options.
Step 3: Choose the comparison unit
After finding the changed lines, choose the unit used to show where they differ within each line.
- Space-separated chunks: good for prose in languages that put spaces between words, such as English or Korean. Comparing the pieces between spaces makes "what changed into what" read naturally, and in Korean, where particles attach to words ("계약은", "계약을"), it keeps a word and its particle together. For Chinese or Japanese, which are written without spaces, the character unit is usually more useful.
- Word: good for English documents and sentences that mix numbers and symbols.
- Character: use it to pinpoint places where only a character or two changed, such as amounts (5,000,000 → 5,500,000), dates (January → March), or clause numbers (Article 3 → Article 4). When long sentences have changed a lot, the highlighting can become fragmented and harder to read.
We recommend scanning the whole document with word or space-separated units first, then looking at lines containing numbers again in character mode.
What to check especially in contracts
Once you have found every change, read the changes in the following categories once more.
| Item | Examples of changes to check |
|---|---|
| Amounts and fees | Figures, units (dollars/thousands), whether tax is included, payment timing |
| Terms and deadlines | Start and end dates, "within" versus "after", business days versus calendar days |
| Parties | Company names, representatives, addresses, and whether the party designations (e.g. Party A and Party B) have been swapped |
| Strength of obligations | "may" ↔ "shall", "will use reasonable efforts" ↔ "guarantees" |
| Liability and damages | Caps, exclusions, liquidated damages rates |
| Termination | Grounds, notice periods, penalties |
| Dispute resolution | Jurisdiction, governing law, arbitration clauses |
| Clause numbers and references | Whether references such as "pursuant to Article 5" still point correctly after clauses were added or removed |
For example, if "Party B may invoice the fee by the last day of each month" becomes "Party B shall invoice…", only a few characters differ, but the nature of the obligation changes. diff makes sure you do not miss small changes like this.
How this differs from a word processor's change tracking
Word's "Track Changes" records only edits made while the editor had the feature turned on. If the other side turned tracking off before editing, or recreated the document as a new file, no record remains. Text comparison only needs the two final documents, so it shows every character that actually differs, regardless of who changed what and how. On the other hand, it does not tell you about formatting changes or who made each change, so using both methods together is the most reliable.
When handling sensitive documents
When you paste contracts, HR documents, or unpublished material into an online tool, you need to know where that content goes. This site processes the comparison only inside your browser and does not send your input to a server. Even so, if your company's security policy prohibits using external websites at all, follow the policy.
Try it in this tool
Press the Example button in the Text Diff Checker to load two short versions of a contract. Switch the in-line diff unit between space-separated chunks and characters to see how the amount and date are marked. The HTML button in the result bar copies a colored comparison table that you can paste into an email or report. The differences between the whitespace options are covered in more detail in Whitespace options, and line-break problems in Line endings and invisible differences.