A free program for iPhone, by Milad Fakhr.

This app lets you edit PDFs. You can draw on the document to change the appearance of the text and image, and you can use the tools to resize them or move them around. You can also add new pages to a PDF, which you can combine with others to make a new document. This also lets you mark up pages or search for specific words or phrases within a PDF.

The app lets you choose from a wide variety of PDFs to work on, including books, scanned documents, and even PDFs of web pages.