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todd8 · 2016-04-15 · Original thread
LaTeX is plain text markup so old LaTeX documents can usually just be read without processing. (The major exception is that graphics are hard to visualize as a sequence of draw commands!). Further, ordinary LaTeX from the last few decades can still be processed without difficulty. The older versions of LaTeX are still available online.

Of course, things are never as simple as they should be. LaTeX is a markup language that through macro expansion ends up expanding into TeX. Since TeX 3.0 in 1989, Knuth has attempted to keep the TeX system stable. Since then TeX documents should produce the same output, pixel for pixel, as they do now running on the current version 3.14159265 (yes, the version number is converging to pi, there won't ever be a TeX 4.0).

Few people, however, produce documents in plain TeX--the LaTeX markup is so much more convenient than the lower level TeX. LaTeX has been slowly evolving and there are some backward compatibility issues, but they are minor. The first release of LaTeX seeing general use was described by Leslie Lamport (the creator of LaTeX) in his 1985 book[1]. That version of LaTeX, 2.09, can still be processed by today's LaTeX 2e in compatibility mode. LaTeX 3 is supposed to supersede LaTeX 2e someday, but it's not clear how many more years that will be.

Since LaTeX is open source the distributions from TUG (the TeX User's Group) are easily obtained and they have all the historical versions of LaTeX and TeX available.

This all makes LaTeX/TeX seem like one of the best ways to maintain a document's source for the future. A few tips:

- Fonts can be a problem because fonts evolve. Either use something like TeX's extensive collection of "built in" Computer Modern fonts or save the font files along with the source of anything that you might want to work on in twenty years.

- LaTeX has a wide number of very sophisticated third party extensions. Along with the document source it would be a good idea to keep the contemporaneous versions the extensions used by the document. (These extensions are just files of additional macros.)

- If one is only interested in the typeset results of a LaTeX document, use a LaTeX extension like pdfx (or Adobe Acrobat) to generate a PDF/A version of the document (LaTeX programs normally generate pdfs). PDF/A is a pdf specification from Adobe that is intended for archival use and rendering far in the future (fonts are embedded in the output, etc.).

- Pandoc can convert LaTeX to a wide number of alternative formats (HTLM etc.) with some success depending on the target language and the document complexity.

[1] http://www.amazon.com/Latex-Document-Preparation-System-User...

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