Why a PDF reader says the seal is not trusted

LulaSign certifies every completed PDF with a digital seal of its own: a PAdES certification signature, "no changes allowed". Open the PDF in Adobe Acrobat or another PDF reader and the signature panel shows it certified by LulaSign Document Seal.

Why it says "unknown" or "not trusted"

Acrobat may say the signer's identity is unknown, or that at least one signature has problems. That is about who made the seal, not about the document. LulaSign makes its seal on its own servers rather than buying it through an outside certificate authority, so Acrobat does not recognise the seal's maker until you tell it to.

What the seal does prove still holds: any change to the file after it was completed breaks the seal, and the reader says so plainly - that the document has been changed since it was certified.

Trust LulaSign's seal on your computer

1. On the verification page of a completed document, choose Download LulaSign root certificate.
2. In Acrobat open Preferences, then Signatures, then Identities & Trusted Certificates.
3. Under Trusted Certificates, import the downloaded file and tick Use this certificate as a trusted root and Certified documents.

Compare the SHA-256 fingerprint the verification page shows with the one in Acrobat's certificate viewer before you trust it. You only do this once per computer.

Check a document without Acrobat

You do not need to trust anything to check a document: Verify a document compares the file with the one LulaSign recorded when it was completed, byte for byte.