Check a signed PDF

Whether a document signed in Longtom has changed since it was signed, who signed it, and when. Everything happens in this page: the file is not uploaded anywhere.

What this checks

• Unchanged. The signature covers every byte of the file except itself. One changed byte, or anything added after signing, and the check fails.
• Who. The name in the signer's certificate. Every Longtom signing key is the signer's own and never leaves their computer. A subscriber's key is also certified by Longtom to their subscription, which shows it belongs to a paying Longtom account; it does not show who the business is. Either way the name is what the signer gave.
• When. With a secure timestamp, Longtom's time-stamping authority witnessed the signature at the time shown. Without one, the time is the signer's own computer clock.

The same checks run in Longtom itself. This page exists so that anybody can make them without trusting Longtom's servers: it uses only your browser's own cryptography, and you can save it and run it offline.