To add a digital certified signature to a PDF using Adobe Acrobat:

Step 1: Obtain a Digital Certificate

You need a digital certificate issued by a Certificate Authority (CA). You can obtain one from a trusted CA like GlobalSign, DigiCert, or VeriSign, or you can create a self-signed certificate using Adobe Acrobat. Note that self-signed certificates are not as trusted as those issued by a CA.

my certificate

My old digital certificate from Comodo has expired. TODO look at CA options again.

1. Let's Encrypt https://letsencrypt.org/
2. ZeroSSL https://zerossl.com/
3. SSL.com https://www.ssl.com/
4. GlobalSign https://www.globalsign.com/en
5. Comodo https://www.comodo.com/

Used Comodo in the past, paid-for.
It was painful & expensive.
Don't use it enough to justify the cost.

Step 2: Open Your PDF in Adobe Acrobat

Launch Adobe Acrobat and open the PDF file that you want to sign.

Step 3: Add a Signature Field (if needed)

If the PDF does not already have a signature field, you can add one by going to "Tools" > "Prepare Form" > "Add a new form field" > "Digital Signature". Click and drag to create a signature field where you want your signature to appear.

Step 4: Save the Document

After adding the signature field, save the document.

Step 5: Sign the PDF

1. Click on the signature field you added.

2. In the "Sign Document" dialog box, select your digital ID (certificate) from the "Sign As" dropdown list. If you don't have a digital ID or want to use a different one, click "Configure New Digital ID" and follow the prompts to create or import a digital ID.

3. Choose your signing method. For a visible signature, you can choose "Create New Appearance" to customize how your signature will look, or select from the default appearances.

4. Enter the password for your digital ID (if prompted).

5. Click "Sign".

Step 6: Save the Signed Document

Save the signed PDF by choosing "File" > "Save As" and selecting a location on your computer. You may want to save the signed document with a different name to differentiate it from the original, unsigned version.

Now your PDF has a digital signature certifying its authenticity.

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