[epc]

IBM tried to push a competitor in the 1990s…BookManager was an initially mainframe (VM/CMS, MVS, etc) combination of viewer program and proprietary format. It came about in response to both IBM customers and product documentation groups demanding some sort of online “hypertext” version of the thousands of publications available.

IIRC it came out around the same time as the initial Acrobat format but not necessarily in response to it. Eventually there were viewers for Windows, OS/2. It wasn't particularly bad, but it was very literal in display and Acrobat/PDF rapidly left it in the dust.

When the web boomed in 1995–1996 the product group behind BookManager tried to ban distribution of PDFs by other IBM groups but failed. One of the problems with BookManager formatted files is you had to recreate the appropriate record format if you transferred it back to a mainframe, and I vaguely recall EBCDIC vs ASCII issues (where PDF is, I think, UTF native?).

https://en.wikipedia.org/wiki/SCRIPT_(markup)#BookManager