# Protection of Signed Documents Against Unauthorized Modification

**Objective**

Once a document is signed or certified, protect it so that any later change can be detected.

**Guidelines**

After a document has been digitally signed or certified:

- Any change to the document must cause the signature validation to fail or clearly show that the document was modified.
- Your system must be able to detect unauthorized changes made after signing.
- No one should be able to add, remove, or change content without that change being detectable.
- It must be possible to verify the document's integrity at any time — today, next month, or years from now.