PDF Tools is, among other things, a replacement of Emacs's DocView for PDF
files.  The key difference is that pages are not pre-rendered by
e.g. ghostscript and stored in the file-system, but rather created on-demand and
stored in memory.  This rendering is performed by a special library named, for
whatever reason, poppler, running inside a server program.  This program is
called epdfinfo and its job is to successively read requests from Emacs and
produce the proper results, i.e. the PNG image of a PDF page.

Actually, displaying PDF files is just one part of PDF Tools.  Since poppler can
provide us with all kinds of information about a document and is also able to
modify it, there is a lot more we can do with it.

WWW: https://github.com/politza/pdf-tools