Given the history between Adobe and Apple, this might be kind of surprising, but it happened anyway. Adobe has released an app for iPhone and iPad called CreatePDF that allows you to make and edit your own PDF files, right on iOS. The app can be used to open up any number of document formats, and then uses Adobe's own conversion services to assemble them however you want into a full PDF document. The app can open everything from Word documents and Excel spreadsheets to images and OpenOffice documents, and converted PDFs can be sent off as email attachments, or even sent to other apps on the iOS device.
The app is available as a $9.99 universal download. It's good to see this kind of thing available -- it just means there's even more functionality for iOS in terms of not just viewing documents, but also building and creating them while mobile.