Early stage, focused only on well-formed input and Type 1 fonts
https://www.adobe.com/jp/print/postscript/pdfs/PLRM.pdf
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf
https://adobe-type-tools.github.io/font-tech-notes/pdfs/T1_SPEC.pdf
http://www.libpng.org/pub/png/spec/1.2/png-1.2.pdf
https://www.adobe.com/content/dam/acom/en/devnet/postscript/pdfs/TN5603.Filters.pdf
https://www.adobe.com/content/dam/acom/en/devnet/actionscript/articles/psrefman.pdf
https://hepunx.rl.ac.uk/~adye/psdocs/ref/REF.html
http://fileformats.archiveteam.org/wiki/PostScript_binary_object_format
http://members.chello.at/~easyfilter/Bresenham.pdf
https://en.wikipedia.org/wiki/Ascii85
https://pomax.github.io/bezierinfo
https://secure.math.ubc.ca/~cass/piscript/type1.pdf
https://ltr.wtf/explained/bidiintro.html
https://speakerdeck.com/ange/lets-write-a-pdf-file
https://web.archive.org/web/20150110042057/http://home.comcast.net/~jk05/presentations/PDFTutorials.html/