ByteScout PDF Multitool* : pdf editor (split, merge, rotate, remove), pdf extractor (table, image), pdf compressor, pdf OCR, pdf converter (image, html), pdf parser
PDFsam Basic: pdf editor (split, combine, merge, rotate)
MuPDF : very lightweight pdf, xps, epub, cbz viewer
Foxit Reader : pdf reader (reflow, rotate), pdf anotation (comment, type, draw, sign, stamp)
SumatraPDF : fast pdf reader
GPL Ghostscript : pdf rendering engine
Free PDF Compressor : pdf compressor
PDF Reader by Xodo : pdf reader (reflow, rotate), pdf compressor, pdf anotation (comment, type, draw, sign, stamp), pdf editor (split, rearrange)
PDF24 : the most complete pdf editor
Latex Editor
MiKTex : LaTex engine
KLatexFormula : LaTex formula editor
TexStudio : LaTex editor
Ebook and Document Converter
calibre : ebook manager
Pandoc : document converter engine (tex, latex, markdown, word, odt)
pandoc-crossref : reference plugin for pandoc
wkhtmltopdf : document converter
Panwriter : GUI for Pandoc (tex, latex, markdown, word, odt)
Citation Manager
Mendeley Desktop : citation manager
Zotero : open source citation manager
Office Suite
LibreOffice : open source office suite (Writer, Calc, Impress, Draw, Math, Base)
Microsoft Office : office suite from Microsoft (Word, Excel, Powerpoint, Access)
Accesibility
Microsoft Learning Tools OneNote Addon : immersive reader
Immersive Reader Offline Extension
Cloud Storage
Microsoft OneDrive
Graphic Editor
Microsoft Visio: diagram and vector graphic drawing and editor from Microsoft
draw.io : graphic editor
Graphviz : graphics and drawing package (library)
Origin
Drawing App
Inkscape: open source vector graphic drawing and editor
Krita: open source vector graphic drawing and editor (digital painting and 2D animation)