PDF Conversion and Reading

Cool PDF Reader

The world's smallest PDF viewer/reader to view, print, and convert PDF files.
https://www.pdf2exe.com/reader.html
Download:
https://www.pdf2exe.com/CoolPDFReader.exe

CutePDF Writer

Create PDF files from any Windows application that supports printing.
https://cutepdf.com/products/cutepdf/Writer.asp
Requires Ghostscript:
https://ghostscript.com/
Download:
https://ghostscript.com/releases/gsdnld.html

CutePDF Editor

CutePDF Editor is a cloud-based PDF application.
Access the Editor:
https://editor.cutepdf.com/

PDFTK Builder & other PDF Resources

PDFTK Builder - Collate, Split, Apply Background to, and Password Protect PDF files.
http://angusj.com/pdftkb/
http://angusj.com/pdftkb/pdftkb_setup.exe

Foxit Reader: Free PDF Reader

Small  and fast PDF reader. There is no longer any need to have Adobe Acrobat Reader installed.
https://www.foxitsoftware.com/products/pdf-reader/
Linux Version: I could not find an official download link on their website (it looks like they have stopped support for Linux) but I found a link from their CDN for Ubuntu and it's derivatives...
Download:
Foxit Reader 2.4.4.0911.x64 (Linux)
More Information: Install & Uninstall Foxit On Ubuntu
https://www.makeuseof.com/install-foxit-pdf-reader-on-ubuntu/