If the error "At least one signature has problems" appears in Adobe Reader, it means that the security certificate used to sign the document in which Adobe reports the error is not a trusted identity in your Adobe reader.

What does the error message mean? 
Update document to Adobe Standards
Make the certificate a trusted identity in your Adobe reader
If making the certificate a trusted identity doesn't work

What does the error message mean?

1. The error message at the top of Adobe Reader says that something is wrong with the signature
2. The signature panel can be accessed by clicking the button on the right, where more details about the actual signing, the certificate used and identity information about the signer appear.
3. In this case, the panel shows that the signature is valid but that the signer's identity is unknown, which is contrary to AATL and the EUTL certificates used for digital signers and the eIDAS regulation.

• The certificate used to sign is not an AATL/EUTL certificate
• The signer's identity is not captured and embedded in the document
• The certificate is not an LTV (Long Term Validation) document - This requires a time stamp for the signature.
  
  

A very common reason for this error, is that the document contains design elements, not supported by Adobe Acrobat. This is usually the case if the document has been created in some other file-editor program, and is then opened in Adobe.

We will now guide you through how to "fix" the document, in order to avoid this issue with future signings.

Update the document to Adobe Standards 

If the PDF was made in an older version of Adobe Acrobat, or some other form of file editing program, Adobe may have an issue validating the signature, as the document is altered once Adobe opens it, with the signature. 

Certain Fonts, colors or images may cause this issue. 



Note - this report code and description, does not always show, even if this issue is the case. 
The following fix does not alter the document in any way that simply signing the document usually wouldn't, but it does ensure that when the document is signed, it will verify the signature correctly. 

1. Open the original Non-signed document, and click File in upper right hand corner
2. Click Print
3. Select the printer: Microsoft print to PDF
4. Click Print. 
5. The document is now saved as a PDF file (again) this time however, any elements that would not have been shown properly by Adobe, (And changed after signing!) are changed to adobe standards. 

The error should now be fixed. 

We will now go through other possible issues, that aren't related to the design of the file.

Make the certificate a trusted identity in your Adobe reader

1. Tap the "Signature Panel" button at the top of your PDF where the error is.
2. Then press "Validate All" in the signature panel on the left
3. In the pop-up that appears, press "OK" to validate all signatures in the document.

Once all signatures are validated, it will display a success message depending on the settings.