Apache PDFBox - The Apache PDFBox™ library is an open source Java tool for working with PDF documents.
iMazing - iMazing lets you transfer music, files, messages, apps and more from any iPhone, iPad, or iPod to a computer, Mac or PC. Manage and backup your iOS device simply without iTunes. (was DiskAid)
iTextPDF - iText offers flexible tools for PDF creation, editing and inspection.
FileBrowser - FileBrowser is a multifunctional file manager for the iOS devices that are used for accessing files in both local and networked environment.
IronPDF - SDK for creating and editing PDFs.
Documents by Readdle - A central hub for all your files.