There are good PDF viewers (e.g. MuPDF), where you need only a minimum of movements for going to a page, e.g. pressing "719g" in order to go to page 719.
Even when a PDF file does not have bookmarks and even when I do not remember the exact page where something is located, I can still know for instance that what I am looking for is about 20% before the end of the book, so if the book has 1400 pages I go quickly to page 1120 and I search around.
With a good PDF viewer I can navigate through a book much faster than I can turn the pages in a physical book.
Nevertheless, one needs to have a big high-resolution monitor in order to come close to the quality of a printed book. The current 4k monitors are a huge progress over the older 1080p or 1440p monitors, but their resolution is still insufficient to match that required to render correctly some of the typefaces that were popular for high-quality printing (but which have been rarely used after the transition to digital typefaces, being replaced by others more tolerant to low-resolution rendering).
Because I read a lot of books, there are almost 10 years since I have last used a display with a resolution less than 4k and I have always used them only at their native resolution. I cannot understand why some people choose to use various scaling methods to make the text big enough (but ugly), instead of doing the right thing, i.e. the rendering of all typefaces at the maximum available resolution, but choosing their dimension in points big enough for comfortable reading (after setting the monitor dots-per-inch value to the true value for the connected monitor).
I agree with your points about PDFs. But what about reflowable formats? The only constant is the rough percentage of where the information might lie. This is a sorry second to a PDF/printed text that also maintains the layout.
Reflowable formats like HTML are a regression over traditional books and I consider them as unsuitable for any document longer than a few pages.
I really hate those who provide some technical documentation in HTML format, without offering a PDF alternative, or at least some other worse format, like EPUB, but which still allows a book-like navigation.
Even on the small display of my phone I still prefer to read books in PDF format, if the reader provides a good UI for pan and zoom, than to read reflowable HTML documents, because with the latter the unpredictability of the layout messes with my ability to remember the location of the information of interest, which is essential when I frequently have to navigate through very long documents.
I like both. Fixed format is great for spatial navigation, diagrams and table (and PDFs usually are better typeset). But for primarily text books (fictions,...) and references, I will take reflowable formats. Both for reading on an eReader (nice on the eyes) and for quick navigation when browsing references (a strong point there for hyperlinks).
Just wanted to drop in to say that this take reveals a blind spot with respect to visual impairment. Reflowability is really vital for visually impaired people who can still see enough to read.
Panning in two dimensions is very cumbersome and brutally inefficient compared to scrolling in just one direction, especially if you have to much of it. If you can only fit a few lines of readable text on your screen at a time, it's really painful to pan across a fixed layout.
(It's been my experience that PDFs are generally not as helpful to accessibility tools as HTML or similar formats can be, as well.)
All of this is exacerbated on displays with slow redraw as well, like e-ink. In the end, I don't even attempt to read comic books or fixed-layout textbooks on my e-readers, for instance. Nobody makes color e-readers big enough for me to read those things comfortably. And my vision is still pretty good— I don't necessarily use fullscreen zoom every day at work and I can still drive.
> the unpredictability of the layout messes with my ability to remember the location of the information of interest
Although technically the layout is fixed, navigation of fixed-layout zoom can itself feel quite unpredictable if you are also using fullscreen zoom, because now you have two layers of independent 2D panning, and all the while your viewport is only a fraction of the screen (in some cases even just 10% of it or much less). At that point, if you're looking at text, you can't see literally any UI elements, just the text. No display corners, no window borders, no title bars, no menu bar, no start menu. All of that spatial positioning you like to navigate by becomes state you have to keep track of in your head, your view of which is updated infrequently at best and only ever partially.
There's also nothing in principle stopping you from using a layout-preserving zoom on reflowable pages. Chrome and Firefox both support this, for instance. By the same token and without loss of generality, you're perfectly free to fix your browser's zoom level and your browser window's size in pixels. It's also trivial to convert HTML to PDF with any of a number of free tools that are easy to get. In contrast PDFs often make spatial navigation the only possible way to navigate, and converting the other way is much harder.
All that said...
> I really hate those who provide some technical documentation in HTML format, without offering [alternatives]
I completely agree with this. Accessibility is intimately related to flexibility, hackability, and ultimately, freedom. Docs should be provided in a way that doesn't assume or support only one way of reading/browsing/working.
I have a pet peeve kinda similar to your complaint, too: I hate it when tools have HTML docs (or even just READMEs or usage messages) but no manpage. Other formats often come in handy for me, too, but I want to be able to view the docs where I'm already using the tool, dammit!
There are good PDF viewers (e.g. MuPDF), where you need only a minimum of movements for going to a page, e.g. pressing "719g" in order to go to page 719.
Even when a PDF file does not have bookmarks and even when I do not remember the exact page where something is located, I can still know for instance that what I am looking for is about 20% before the end of the book, so if the book has 1400 pages I go quickly to page 1120 and I search around.
With a good PDF viewer I can navigate through a book much faster than I can turn the pages in a physical book.
Nevertheless, one needs to have a big high-resolution monitor in order to come close to the quality of a printed book. The current 4k monitors are a huge progress over the older 1080p or 1440p monitors, but their resolution is still insufficient to match that required to render correctly some of the typefaces that were popular for high-quality printing (but which have been rarely used after the transition to digital typefaces, being replaced by others more tolerant to low-resolution rendering).
Because I read a lot of books, there are almost 10 years since I have last used a display with a resolution less than 4k and I have always used them only at their native resolution. I cannot understand why some people choose to use various scaling methods to make the text big enough (but ugly), instead of doing the right thing, i.e. the rendering of all typefaces at the maximum available resolution, but choosing their dimension in points big enough for comfortable reading (after setting the monitor dots-per-inch value to the true value for the connected monitor).