Foxit Reader is a lightweight, fast PDF Reader.

Nitro Software, Inc. develops commercial software used to create, edit, sign, and secure Portable Document Format (PDF) files and digital documents.

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

jPDF Tweak is a Java Swing application that can combine, split, rotate, reorder, watermark, encrypt, sign, and otherwise tweak PDF files.