Emacs-Elements has a nice demonstration on using Emacs’ DocView to read PDF files. One of the nice things about DocView—as opposed to PDF Tools—is that it can read PS, DVI, Djvu, and ODF files as well as PDF files. The downside, of course, is the way it works. When you open a document with DocView, it uses an external tool to render it as one or more PNG files. That can take a few seconds for a long document but more importantly—for me, at least—is that the PNGs are cached. That makes it speedy to reopen the document but it clutters up your file system unless you manually delete the cache.
The video shows how to configure DocView and integrate it with Bookmarks+ to make it easy to locate and open documents. It turns out that you can use any of three external programs to render PDFs into PNGs and the video has some advice on which to use.
Most of the rest of the video demonstrates how to navigate through a document and do things like extracting a rectangular region. DocView is surprisingly featureful and you can see some of that in the video.
If you can’t get PDF Tools working or don’t want to bother trying, DocView is a builtin solution that works well. Its main deficiency, as compared to PDF Tools, is that you can’t annotate the PDF.