PDFpen - PDFpen is a PDF editor to add text, images, and signatures to PDFs.
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.
Adobe Reader - Adobe Acrobat Reader is a free tool for viewing documents that have been stored in Adobe's Portable Document Format (PDF).
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.
Wondershare PDFelement - All-in-one PDF editor
CutePDF - CutePDF is a simple but entirely powerful PDF files creator, converter, and virtual printer.