How can I sign a digital document without needing to print it?

We'll start with the how.

You start by scanning an image of your signature. Just "sign" a white piece of paper, scan it at high resolution, and then using an image editing tool crop it and create a few copies at different resolutions. If you want to get fancy, set the background as transparent.

For reasons I'll describe below, you'll want to keep these files secure.

Ultimately, though, all these files are is an image, a picture, of your signature. If you get my weekly newsletter you'll see that I "sign" my first name at the end with exactly such a picture:

Next, you'll need to be able to edit the document you've received. There are various PDF editing programs out there, and most will allow you, at a minimum, to place, or copy/paste, an image into the PDF document and then save it. A couple of examples include the full Adobe Acrobat tool (not the reader, but the full Acrobat PDF creation tool) as well as Foxit software's PDF Editor (they also make the free Foxit PDF Reader, but the PDF editor is not free).

And that's exactly what you'd do. Insert the image of your signature, or copy it from your image editing program and paste it, into (a copy of) the original PDF document. Choose the right size of signature image so that it looks natural, and place it at or above the signature line in the document. Save the result, and you have a "signed" document.

For completeness: I've also heard of people playing games with screen capture software when PDFs are not editable. Depending on the software used, they capture "screen shots" of the affected pages, alter them as needed in an image editing program, and reconstruct them into a new document that they then print to PDF. After all that, though, it would just be easier to print to paper, sign and scan.

Now, the more practical aspect.

I need to preface this by saying "I am not a lawyer" - because, yes, we're actually treading into some legal areas. These are my opinions and understandings, and not at all intended to be legal advice. Check with your own counsel.

With my behind thus covered...

I've always been under the impression that for many transactions a FAXed signature is as binding as the original.

That scares me.

Because everything we've done above to "sign" a document and send it along above with a copy of your own signature could be done using someone else's signature. Scan a copy of their signature from public records or even a check, clean it up and crop it a bit, and you've got someone else's signature that you could copy/paste into just about any document, and then FAX on.

Now, the good news here is that I think things are changing. In some recent cases when I've signed documents digitally, or offered to FAX in such a document, I've been required to provide the original as well. The bad news is that even a printed version with the digitally pasted signature is often accepted as valid.

Depending on the industry you're in, the use of a digitally inserted signature image may not be understood and thus never even considered, may be understood and accepted, or may be understood and explicitly not accepted if detected.

The question boils down to: can they notice, and if they notice will they care?

And if it turns out they care, will you?

Finally, you can now see why I suggested you keep your scanned signature image secure. You don't want someone else to use it. While it's possible that someone could get your signature from other sources, there's no reason to make it easy.

(One important clarification: a digitally inserted signature image is not the same as a digital signature. The former is simply placing a picture of your handwritten signature into a document, the later is a cryptographic calculation based on the document content and your cryptographic private key or certificate.)