Digital certificate signature cannot verify the identity of document verifier because the signature validity of digital certificate is unknown. The specific steps to solve this problem are as follows:

1. First, we open the Internet option of the computer browser.

2. Select the "Advanced" option on the Internet option setting menu.

3. Find "Allow running or installing software even if the signature is invalid" in the Settings window.

4. Then click Apply, and then click OK.

5. After you finish, you need to restart your computer for the settings to take effect. After restarting, it can solve the problem that the digital certificate signature cannot verify the identity of the document verifier.