Add invisible digital signatures in Word, Excel, or PowerPoint

To protect the authenticity of a document's content, you can add an invisible digital signature. Signed documents will have the Signatures button at the bottom of the document. In addition, for signed documents, signature information appears in the Info section of the Backstage view.

1. Click the File tab. The Backstage view appears.
2. Click Info.
3. In the Permissions section, click Protect Document, Protect Workbook or Protect Presentation.
4. From the menu, select Add a Digital Signature.
5. Read the Microsoft Word, Excel, or PowerPoint message, and then click OK.
6. On the Sign dialog, in the Purpose for signing this document box, type the purpose.
7. Click Sign.

After a file is digitally signed, the Signatures button appears, and the file becomes read-only to prevent modifications.

The following image shows the Protect Document options.