How to capture an old abandonware software manual page to PDF, from the deeply buried Internet Archive ‘Wayback’ copy, without the header frame and other unwanted items on the page.
1. Make your selection(s) on the Web page, by the usual click / drag / select.
2. Crtl P on the keyboard, or Menu / Page / Print to open the browser’s printing preview.
3. Choose More Options / Selection Only. Print to PDF.
There are free Web browser add-ons that also let you make multiple selections on the same page, if there is some cruft that you want to skip.
I assume here that your target manual was at one time posted as a single long Web page, as was a common practice ‘back in the day’ for plugins and utilities. For multiple pages you would save them as individual PDFs and then join these into one. (Capturing complex nested manuals for big software, with sidebar panels and many pages, is another matter. But even they can be wrangled to a single PDF in various ways).
Why do this? Because then the clean and streamlined result can be uploaded as a PDF manual to the main Internet Archive, where it will become visible in search-engines.