Upload the original and the revision. Get a redlined PDF, a synced side-by-side view and a list of every difference with page numbers. Check a lease before you sign it or run a whole review team's contracts, labels and specifications through it.
The engine was built for FDA drug-label surveillance, where a missed change is a compliance failure. It brings the same discipline to any two versions of a PDF.
Paragraphs are aligned across the two documents before comparing, so one inserted sentence is reported once, not as a hundred shifted lines.
Repeating headers, footers and page numbers are excluded. Unchanged tables are recognised and held out. Two-column pages are read in reading order.
Text changes, moved paragraphs, formatting changes and whitespace are classified separately, so reviewers can hide what they do not need.
Every comparison produces a marked-up PDF for the file and a standalone side-by-side HTML view with synced scrolling.
The diff is rules-based, not model-based. The same two documents always give the same result, which is what validation and audit require.
One HTTPS call returns changes as JSON with page numbers, old text and new text, plus the redline PDF. Wire it into a DMS, PLM or approval workflow.
Anyone holding two versions of the same document can find out exactly what changed, whether it is one rental agreement or a thousand contracts a month.
Compare the lease, loan offer, insurance policy or job offer you were sent against the earlier version before you sign. Free, no account, nothing stored.
Compare thesis drafts, a preprint against the published paper, or two editions of a syllabus or guideline and see every edited sentence.
Check a client's returned contract, quote or purchase order against what you sent. Catch a changed price, deadline or payment term in seconds.
Redline counterparty drafts, verify execution copies and keep an audit trail of every revision. See industries.
Call one REST endpoint with two PDFs and get the change list as JSON, a redlined PDF and a side-by-side view. Read the API docs.
Volume pricing, an SLA, and private deployment in your own cloud or data centre for documents that cannot leave your network. See plans.
Industries do not want PDF comparison for its own sake. They want change detection, approval control and an audit trail.
Loan agreements, sanction letters, KYC documents, credit policies
Detect unauthorised changes before a document is signed or filed →Contracts, amendments, NDAs, agreements, court filings
Find every clause modification the other side made, including the ones not mentioned in the cover email →Specifications, BOQs, tender documents, method statements, drawing sheets with text
Revision control on documents that drive cost and safety →Product labels, SOPs, protocols, regulatory submissions, CMC documents
Compliance and an audit trail for every revision →Engineering specifications, work instructions, manuals, supplier documents
Revision control across plants and suppliers →Policy wordings, endorsements, schedules, reinsurance treaties
Detect changes to coverage, exclusions and terms →Sale agreements, leases, title documents, builder-buyer agreements
Catch changed terms before signing →Tenders, RFQs, corrigenda, bid documents, purchase contracts
Detect changed requirements between tender versions →Maintenance manuals, operations manuals, procedures, airworthiness documents
Safety-critical revision control →Component specifications, supplier documents, homologation files, CAD-exported PDFs
Engineering revision control with suppliers →Trial protocols, amendments, investigator brochures, informed consent forms
Version control with a reviewable audit trail →Regulations, notifications, tender documents, policy circulars
Track amendments to long documents →Employment contracts, offer letters, policies, handbooks
Detect changed terms in returned documents →Send two PDFs, receive a change list, a redlined PDF and a side-by-side view in one response. Authenticated with an API key, sized to your volume, with a private deployment option for documents that cannot leave your network.
curl -X POST https://api.simplefiletools.com/api/v1/compare \
-H "X-API-Key: $PDF_COMPARE_KEY" \
-F "old=@agreement-v1.pdf" \
-F "new=@agreement-v2.pdf" \
-F "output=json"
{
"summary": {"insertions": 8, "deletions": 7, "formatting": 0},
"changes": [
{"id": 0, "kind": "replaced", "level": "substantive",
"old": "twelve (12", "new": "twenty-four (24", "page": 1},
...
]
}Files are processed in memory for the duration of the request and discarded when the response is sent. There is no document store to breach.
All traffic runs over HTTPS. API keys are compared in constant time and can be rotated on request.
For banks, pharma and government, the engine can run inside your VPC or on-premises with no outbound traffic.
Practical guides on comparing documents in the industries that need it most.
Preview cannot compare PDFs. Three ways to find the differences between two PDF files on macOS, from free browser tools to Acrobat and the Terminal.
Read →Windows has no built-in way to compare PDFs. Three options that work on Windows 10 and 11: a free browser tool, Microsoft Word, and Adobe Acrobat Pro.
Read →You do not need an app to compare two PDF files on your phone. How to find every change between two versions on iPhone, iPad or Android in the browser.
Read →Yes. Documents up to 30 pages can be compared free with no account and no sign-up. A free account adds five comparisons a month on documents up to 100 pages. Paid plans are only for higher volume, larger documents and API access.
No. The comparison runs in your web browser on Windows, Mac, Linux, Chromebook, iPhone, iPad and Android. There is nothing to download and no plugin to install.
The tool compares PDFs. To compare Word, Google Docs, Pages or Excel files, save or export both versions as PDF first (File, then Save as or Download as PDF) and upload the two PDFs.
Text is extracted from both PDFs with its position and style, repeating headers and footers are removed, paragraphs are aligned between the two documents, and the aligned text is compared character by character. The result is a list of insertions, deletions, moves and formatting changes, plus a redlined PDF and a side-by-side view.
No. Both files are processed in memory for the duration of the request and discarded as soon as the response is sent. Nothing is written to permanent storage and nothing is used for any other purpose.
The engine compares the text layer of a PDF. A scanned document that has been through OCR works; a pure image scan with no text layer does not. When an OCR layer is detected, formatting differences are ranked low so they do not hide real changes.
A pixel overlay flags every page where anything moved, including reflowed text after a one-word insertion. This engine aligns content, so a single inserted sentence is reported once, as one change, even if it shifts every page after it.
Yes. One HTTPS call with two PDFs returns the change list as JSON, the redlined PDF and the side-by-side HTML. See the API documentation for examples in curl, Python and Node.
Yes. Enterprise customers can deploy the engine inside their VPC or on-premises so documents never leave their network. Contact us for details.
Book a 20-minute demo with two of your real revisions, or request an API key and integrate this week.