Just in case my immediately prior response to "Equations on the web" made
the Adobe Acrobat software sound like nothing more than an MS Word add-in,
let me add that the button it adds to MS Word is very nice, but Acrobat
works with any software that can print to a printer through the OS. So if
you use Word Perfect, Acrobat is just as good as if you use MS Word.
Similarly for any spreadsheet, CAD software, electronics simulation (if it
can print the circuits it lets you build), etc.
Adobe accomplishes this trick by making the Acrobat software install a
virtual printer on your machine. When you are ready, select the virtual
printer as the print destination, and it spits out a pdf file.
I've not tried these, but I believe the Acrobat software allows you to add
to pdf files links to Web documents, and pdf documents are word searchable.
These make pdf just about as good as HTML, though I find the switch to a
different interface when the Acrobat reader runs a bit jarring.