Hi ISO_Man.
Do be careful with SignRequest, I have had a quick look over their website they say nothing about being 21 CFR Part 11 compliant (This is the US Cofe of Federal Regulations that governs electronic signatures). Also none of the companies states to be using the software are medical device or appear to be in heavily regulated industries. Before omitting to them you will want to speak to them to ensure the software is compliant to the applicable regulatory requirements you work within.
Also to answer in party Marc's question above Adobe, they offer a package called Adobe e-Sign this is Part 11 compliant. Just using Adobe Pro with a "sign" button, I do not believe is, as it lacks some of the control Part 11 requires.