Signing PDFs

When people talk about signing PDFs, they can mean two things: attaching a digital signature to the file or placing a graphic representation of their signature on the document. Often what people really want to do is the latter.

I got interested in doing the former after reading a Macworld article on signing electronic documents. Everything went well until I attached my first signed PDF to a Mail document... and the signature wasn't showing. I opened the document in Preview and found the same: no signature. But the signature showed up just fine in Acrobat Pro.

Turns out that Apple's version of PDF doesn't support digital signatures. Whether or not that's the reason the "wet ink" (graphic) version of the signature doesn't appear, it's certainly why Preview won't validate the signature cryptographically. You'll need Acrobat/Reader for that.

In my case and, as I noted above, that of most others, I just needed the image to show, regardless of the PDF viewer. Turns out there's an easy way to do that: the stamp feature found in Acrobat Pro.

Go to Tools > Comment & Markup > Stamps and select Create Custom Stamp... Browse to and select the image of your signature that you'd like to use and click OK. Select or create a new category (like Signatures), give the stamp a name, and (I'd recommend) uncheck Down sample stamp to reduce file size. Click OK.

To use your new stamp, go to Tools > Comment & Markup > Stamps > Signatures (or whatever category you chose) and select your stamp, then move it into position.