Yes, I understand your concern. Adobe Reader on an Apple product is somehow, just not right. But give this one a try before you bash it. Adobe Reader of iOS is free and I found it painless to use. It does signatures and and basic annotation on PDF documents.
Here is a review from today in TUAW by Kelly Hodgkins:
Adobe updated its Reader app for iOS, and what was a good PDF reader is now an excellent tool to annotate and sign documents. As luck would have it, I needed to add a note and sign a PDF file that was sent to me via email today. This rare occurrence gave me the opportunity to check out these new features using the iPad version of the Reader app.
The latest version of Adobe Reader has several new tools for marking up a document including a freehand drawing tool, a highlighter, strikethrough, and underline. You can take a page in a PDF document and use these tools to point out spelling errors, highlight important text, mark sections for deletion and more. If you need to add a longer correction, you can even attach a sticky note to any position in the document.
Besides annotation, there’s a new form feature that lets you toggle radio buttons or select a text field and start typing in text. A new signature feature aso lets you add your signature and place it anywhere in a document. Your placement has to be good, because once you set the signature down on the page, you can’t move it.
Overall, Adobe Reader is an excellent tool for someone who doesn’t need advanced features like Dropbox backup. If you only need to mark-up or add a quick signature to a PDF file, then you can’t go wrong with Adobe’s software. It’s available for free from the iOS App Store.