PDFtk - The PDF Toolkit
PDFtk is a simple tool for doing everyday things with PDF documents. It comes in three flavors: PDFtk Free, PDFtk Pro, and our original command-line tool PDFtk Server.
PDFtk 
Use PDFtk Pro to quickly split, merge, rotate, watermark, stamp and secure PDF pages and documents. PDFtk Pro is a graphical application that makes working with PDFs as easy as possible.
Power Users: PDFtk Pro comes with our command-line tool, PDFtk Server. So you get both the GUI and the command-line interface to PDFtk!
Only $3.99! Now Free! (limited time offer)
In celebration of the 20th anniversary of pdftk, we are making PDFtk Pro available for free! Meanwhile we are working on a new release of pdftk which will be faster and more portable. Thank you for your many years of support! This is a limited time offer.
Available for Windows 10 and 11:
End-User License Agreement
Conditions for using PDFtk Pro are detailed in its End-User License Agreement here. PDFtk Pro uses third-party libraries that have their own licenses which are described here under Third-Party Materials. This license information is also included with the downloaded software.
PDFtk 
PDFtk Server is our original command-line tool. It is commonly used for server-side processing of PDFs. It is also used by many PC software publishers to give their products the ability to manipulate PDFs.