"The original document is 68,608 bytes and file on my Mac says it's a Microsoft Word for Macintosh 4.0 file. That matches with TBL's note on the W3C page saying: 'A hand conversion to HTML of the original MacWord (or Word for Mac?) document written in March 1989 and later redistributed unchanged apart from the date added in May 1990.'

Microsoft Office for Mac came out in 1989. That was Microsoft Word 4.0 so we're looking for compatibility with Microsoft Word for Macintosh 4.0. Let's see what modern software can open this."

https://blog.jgc.org/2024/02/the-original-www-proposal-is-word-for.html