Readdle has PDF Expert 5 (iTunes Link) for the iPhone, iPod Touch, iPad in the iTunes App Store for FREE (regularly $9.99) for a limited time.

PDF Expert 5 is a must-have app for anyone who reads, annotates or edits PDF documents on iPad or iPhone. It allows you to mark up documents with highlights and handwriting, insert text and stamps, sign and even merge PDFs. Moreover, PDF Expert 5 is the best choice for filling out PDF forms right on your iPad and iPhone.

You can open various file formats such as iWork, MS Office, PowerPoint, text files, images, even music and video files, etc. Get these files from desktop computers, email attachments, documents on Dropbox, OneDrive, GoogleDocs and “Open in” from other applications.

PDF Expert 5 provides the best experience for filling out PDF forms. Text fields, checkboxes, radio buttons and other form elements work as you expect and all the information you enter is saved within the form. Even complex interactive forms with Javascript work impressively well.