How do I add a signature to a word or .pdf document?

I almost never disagree with Palcouk, but I strongly advise against ever including a picture of a signature as a way to authenticate and sign any document. Pictures of signatures can be copied exactly and placed onto any other document. Using a picture of a signature is an open invitation to forgery. If you ever allow a picture of your signature to be used as authentic, then you'll be hard pressed to deny your signature on all other documents.

Microsoft Word does not offer a digital signature option. You can control how a document is used by going to the Review tab of the Ribbon and clicking Protect > Restrict Permission and setting options there.

To add a real digital signature you must first save your document as PDF and then use Adobe Acrobat (not free) or Adobe Acrobat Reader (free) to make a digital certificate and affix the digital signature to the PDF.

In Acrobat or Acrobat Reader, click the More button in the Tools column and choose Use a Certificate.

In the next dialog choose Digitally Sign.

What happens next depends on whether you have already created a digital certificate. If you already have at least one certificate, the next dialog will let you choose the certificate and then you drag a rectangle in the document where you want the signature to appear. If you don't already have a certificate, then you'll be prompted to make one. Making a certificate is easy, but please do not use the option to include a picture of your signature. That defeats the whole purpose have having a digital certificate.

https://support.microsoft.com/en-us/office/insert-a-signature-f3b3f74c-2355-4d53-be89-ae9c50022730#ID0EBD=macOS