1. sign pro PDF prepares any document for secure electronic signature capability

  2. Convert PDFs to forms and let people fill them easily

  3. LightPDF is the best free online PDF tool that allows you to edit and convert PDF.

  4. OpenSignature is an open source project for the digital signature of documents.

  5. jPDFProcess – Java PDF Library to Create, Manipulate PDF      jPDFProcess is a Java library to create and manipulate with PDF documents that can be used to deliver customized PDF content to your users or to process incoming PDF content.

  6. JSignPdf is a Java application which adds digital signatures to PDF documents.

  7. PDFTools

  8. jPDF Tweak is a Swiss Army Knife GUI application for PDF documents: combine, split, rotate, reorder...

  9. Advanced PDF Utilities Free helps deal with PDF files such as to merge or split pages, convert PDF to text & convert image to PDF or vice versa.

  10. PyPDF2 - A utility to read and write pdfs with Python

  11. Edit PDF files with our feature-rich PDF Editor. Download Foxit PDF Editor to convert, sign, scan / OCR & more. A speedy PDF Editor alternative to Adobe Acrobat.

  12. PDF Mod is a simple application for modifying PDF documents.