Dangerzone
Dangerzone – Convert PDF files, office documents or images to safe PDF files. Free and open source program
NightPDF
NightPDF is an application that allows you to read PDF files in dark mode. Free and open source program
Master PDF Editor
Master PDF Editor is a free and multi-platform, easy-to-use, but powerful and multifunctional program for working with PDF documents
Boomaga
Boomaga is a virtual printer for viewing a document before printing it out using the physical printer
qpdfview
qpdfview – free and open source software for viewing PDF documents with tab support
Okular
Okular is a free and open source, multi-platform document viewer that supports a variety of formats
Evince
Evince is a free and open source program for viewing PDF documents, comic books, and others.