Don't believe there are any apps for creating PDF. Reading, yes. Annotating, yes, creating? Not something Apple is interested in given their tenuous relationship with Adobe.
You should take a look at Save2PDF. It lets you create, edit, merge, and wirelessly print .pdfs.
You can edit the pdfs, but I don't believe you can sign the .pdfs using a stylus. For more details on the features, there's an in-depth review of this app on PC Mag here.