A 5,000-page PDF book??? Where on earth did you get that? Who the heck wrote something like that? Never mind. You need speed reading training. speed reading - Google Search
As for reading online, read at the rate you use for real-life reading. But don't get hung up on what other people are doing. If you're going to try to read in a way that's different from how your eyes really work, you might as well just read something you enjoy. The only way to really achieve comprehension (even though it feels like it's harder) is to actually sit there and read while doing it, because then you'll be looking down at it at the same time your brain is looking up and understanding it — and thus, understanding a lot more. The only way to really achieve comprehension (even though it feels like it's harder) is to actually sit there and read while doing it This “you're a lot faster” crap is annoying — but if you know how much you're getting wrong, you're not going to be able.