V4 and before exists (AFAIK) only on paper
By the time of V4, most all of the manuals were being maintained
internally in VAX DOCUMENT. It's fairly standard SGML, although
there were some specialized macros used just for DEC-ish look and
feel at the presentation.
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Those that weren't VAX DOCUMENT were DSR (Runoff).
On their way to paper the VAX DOCUMENT source was turned into
postscript. Some layered products came with postscript release
notes and electronic documentation (usually bookreader but
sometimes flat text and sometimes postscript.)
Tim.