Sign icon is greyed out

Hello, I need help signing a form for an end-user. The form shows the following in Security Properties:

Document Security

This document's security method restricts what can be done to the document.

Security Method: No Security

Can be Opened by: All versions of Acrobat

Document Restrictions Summary:

Printing Allowed

Document Assembly: Not Allowed

Content Copying: Allowed

Content Copying for Accessibility: Allowed

Page Extraction: Not Allowed

Commenting: Not Allowed

Filling of form fields: Allowed

Signing: Allowed

Creation of Template Pages: Not Allowed

I've tried openning it in Acrobat Reader DC, Acrobat X, Adobe Reader XI. Sign is greyed out everywhere.

Note:

There isn't a field labelled "Signature" but there is a "Name" field.

He used to be able to sign these documents from the same client

Discussion moved from Acrobat Reader to Security & Digital Signatures by moderator

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