how to edit a digital signature

I think what we have here is a failure to communicate.

Let's start with some terminology so we can be on the same page.

Digital ID: A Public Key Certificate paired with a private key that is used to create a digital signature. Analogous to a pen in the real world.

Digital Signature: A cryptographic blob of data embedded in the document that assures document integrity and signer identity. The digital signature can be either invisible, or visible. Analogous to a wet ink signature in the real world.

A Visible Digital Signature: The pictographic representation of the actual signature blob. It is comprised of a background image (Acrobat uses the pink trefoil by default) and a foreground image. The foreground may be divided in half, with the left side containing a graphic image and the right side text that contains information from the actual signature.

Custom Signature Appearance: A preference that allows the signer to configure the look and feel of a visible digital signature.

My guess is you want to create a custom signature appearance so that when you do apply a digital signature to the PDF file it's using an image of your actual wet ink signature. To do that select the Edit > Preferences menu item (Win) or Acrobat > Preferences menu item (Mac). Select Security from the Categories list box and the click the New button in the Appearance group box. From there you can import a file that contains your scanned wet ink signature and control which items you want displayed in the visible signature field.

Steve