PDFpen - PDFpen is a PDF editor to add text, images, and signatures to PDFs.
iTextPDF - iText offers flexible tools for PDF creation, editing and inspection.
Adobe Reader - Adobe Acrobat Reader is a free tool for viewing documents that have been stored in Adobe's Portable Document Format (PDF).
Apache PDFBox - The Apache PDFBox™ library is an open source Java tool for working with PDF documents.
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.
IronPDF - SDK for creating and editing PDFs.