ECA, you obviously have a serious issue with PDF and almost seem to argue anything BUT
PDF, rather than look at PDF's advantages.
HTML would mean having all of the text converted to real text, plus having to create the page all over again from scratch. The idea here is to preserve the original document, not to re-create it! Word processor, text editor and HTML variations all would mean creating the original manual all over again and that bypasses the objective completely (if only for the sake of NOT using PDF).
RTF and Word documents are more platform-specific than PDF is.
And as has already been stated, just using JPG format would mean multiple files (which is superseded by the PDF format being in one portable document), plus the fact that most manuals are in black & white, which using JPG would be overkill for with it's full 24-bit palette and compression artifacting. And before it is suggested, a combination of formats (GIF, PNG, JPG, etc.) is also a sloppy, impractical solution. PDF is the industry standard not only for archiving manuals (its usage gets stronger every day), as well as manufacturers using the PDF format for the manuals included in online distribution of their software.
Denying this is just being stubborn. Likewise with your seeking a lower resolution than 300. I suppose there were those that were chagrined at advancing past 640x480x256 graphics resolutions as well (at the time it required more memory, not as compatible, etc.) but thankfully, the pioneers moved forward to more realistic pastures. PDF is without question the only format to fill the needs of this project.
I HATE PDF. Only for 1 good reason. Those that USE it, dont clean it up, and use ONLY what is needed. They tend to be VERY slow, and 10-100x TEXT format.
You really can't make a global generalization that those who create PDF's don't clean it up. That's like saying nobody should use HTML or Flash because nobody writes clean pages with them. Mind you, there are many who don't make good PDF's. Part of that is a flaw of Adobe (if you crop portions of a PDF file internally, it keeps the uncropped portion stored for some odd reason...no way around this stupid flaw, either). But there are tools that will convert image text to real text, thus reducing file size, as well as allowing search/copy/paste functions in/from the document.
The slowness of a PDF is not moreso than any other file format...it all depends on the data herein and the speed of the system it is displayed on. Here at work, we can get a PDF that is 3-4 megs big (that when converted to EPS will exceed 200 megs sometimes!) for a page that is 21.5"x13" and it opens faster than any web site or Word document.