How this works in your browser
Both documents are rendered independently by PDF.js into two canvases in your browser, and the panes share a scroll position so equivalent pages stay aligned as you move down. Rendering rather than diffing is a deliberate scope choice: a genuine comparison would need either pixel differencing, which flags every reflowed line as a change and drowns you in noise, or semantic text alignment, which is a substantially harder problem. Presenting the two faithfully and letting you judge avoids both failure modes. It also means scanned documents work exactly as well as digital ones here, since everything is being drawn as an image regardless.
Compare PDF vs. traditional online converters
| Feature | Compare PDF (in-browser) | Traditional online converters |
|---|---|---|
| File upload required | No - never leaves your device | Yes - file is sent to a server |
| Processing queue | None - starts instantly | Often, especially at peak times |
| Watermark on output | Never | Common on free plans |
| Usage limits | None - free, unlimited use | Often capped per day or file size |
| Works offline once loaded | Yes, for most tools | No - requires a live connection |
| Account required | No | Often, for anything beyond a trial |
How to use Compare PDF
- 1
Open the Compare PDF tool
Go to tools.slaytic.com and open the Compare PDF tool. No sign-up or account required.
- 2
Load both versions
Add the older document in one pane and the newer one in the other. Neither file leaves your device.
- 3
Scroll through in sync
Move through both documents together to spot layout, text and image changes, scrolling independently where page counts differ.
Common ways to use Compare PDF
Reviewing contract revisions
Put the version you signed next to the one returned to you and check the pages that matter.
Checking a print proof
Confirm a final print-ready file matches the proof that was approved before it goes to press.
Auditing report versions
Compare last quarter's report against this quarter's to see what moved, was added or was dropped.
Frequently asked questions
Does it automatically highlight differences?
The current version shows both documents side by side for visual comparison. Automatic pixel-diff highlighting is on the roadmap.
What if the documents have different numbers of pages?
Both documents are scrolled independently. If one is longer, you can scroll it separately to compare the extra pages.
Can I compare scanned PDFs?
Yes - scanned PDFs are rendered as images in both panes. Differences in scan quality or skew may make comparison harder, but the side-by-side view still helps.
Will it find changes for me?
No, and it is worth being clear rather than implying otherwise. This is a synchronised side-by-side viewer: it puts both versions in front of you and keeps them aligned, but you do the spotting. Automatic difference highlighting is not implemented yet.
What is this actually good at?
Catching structural and visual changes quickly: a clause that moved, a table that gained a row, a logo that changed, a page that was inserted. It is far weaker for a single altered word buried in a paragraph, which the eye slides over.
How do I compare a document that is text-heavy?
Run both versions through PDF to Text and compare the two text files in any diff tool. That catches word-level edits reliably, which visual comparison will not.
Are either of my files uploaded?
No. Both documents are rendered inside your browser tab, which matters when comparing contract drafts.