Check a signed PDF

Whether a document signed in Longtom has changed since it was signed, who signed it, and when. The check runs in this page; the file is not uploaded.

What this checks

• Unchanged. The signature covers every byte of the file except itself. One changed byte, or anything added after signing, fails the check.
• Who. The name in the signer’s certificate, as the signer gave it. Every Longtom signing key is the signer’s own and stays on their computer. A subscriber’s key is also certified by Longtom, which shows it belongs to a paying Longtom account but not who the business is.
• 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.

Longtom runs the same checks. This page lets anyone make them without Longtom’s servers: it uses only the browser’s own cryptography, and can be saved and run offline.

Longtom’s certificates

• Time-stamping authority (tsa-2026-10-09.cert.der)
  SHA-256 1b01d0bca987a99620a247e4203d183eaeefaf2c8db1c8a3efe30f9675c8a7f5
• Device certificate authority (ca-2026-10-09.cert.der)
  SHA-256 acde38159180c62343c6bc44a7dd8306d4effa9596be772c34a48b2a73b2166c