Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
GroupDocs - GroupDocs is a web-based service for online document sharing, collaboration and management.
Adobe Acrobat DC - Make your job easier with Adobe Acrobat DC, the trusted PDF creator. Use Acrobat to convert, edit and sign PDF files at your desk or on the go.
FileProInfo - It's All About Files, Software, Online Tools - 100% Free
Wondershare PDFelement - All-in-one PDF editor
File-Extensions.org - Large computer file extension library with detailed explanation of each file type with links to download free or associated software programs.