PDF-XChange Viewer is a free PDF editor/reader.

PDF Studio is a multi-platform PDF editor.

Foxit PhantomPDF provides you with a full suite of PDF viewing, sharing, and editing features.

PDF-Tools is a flexible & power wizard-driven application for batch creating, manipulating, and modifying PDF files.

Adobe Acrobat Reader DC is the industry standard for viewing, printing, signing and commenting on PDF documents.

Nitro Pro gives you the tools to do more with your documents.

K2PDFOPT optimizes PDF/DJVU files for mobile e-readers.