If you're reading a pdf with multiple pages, zooming out to show the entire page (or even displaying two pages at once if your display is wide enough) enables super-fast scrolling through the document. I have seen people not do this and it was painful to watch.
Also, some pdf readers (including adobe reader) have a "magnifying glass" feature, which achieves what you described without having to open the document a second time.
Oh god, the scrolling, the cumative man-hours I've wasted. How did I never see this before.
This is the first post of the 2015 repository rerun, which appears to be a good idea. The motivation for this rerun is that while the 12 repositories (go look them up, they're awesome!) exist and people might look them up, few new comments are posted there. In effect, there might be useful stuff that should go in those repositories, but is never posted due to low expected value and no feedback. With the rerun, attention is shifted to one topic per month. This might allow us to have a lively discussion on the topic at hand and gather new content for the repository.
The first repository to be rerun is the Boring Advice Repository, because of... on a whim.
Enter original motivation (by Qiaochu_Yuan):
The Boring Advice Repository is filled with lots of diverse advice, I've summarized some of it in a comment below.
So what should go here? To go with Qiaochu_Yuan again (adding emphasis):
I don't know if you should post new advice here or in the original repository. Perhaps search the old repository with ctrl+f (when on windows) and if you don't get results, post it here.