When comparing qpdfview vs (Spac)emacs with pdf-tools, the Slant community recommends qpdfview for most people. In the question“What are the best PDF viewers for Linux?” qpdfview is ranked 5th while (Spac)emacs with pdf-tools is ranked 14th.
Ranked in these QuestionsQuestion Ranking
Pro Low on resources
Pro Reloads on changes instantly
Pro Outline, properties and thumbnail panes
Pro Open multiple pdfs in tabs
qpdfview is a tabbed document viewer.
Pro Allows for some scripting
Opens files in named instances, open files on designated page.
Calling of userscripts on a document is thus far not possible.
Pro Fast search in all opened files
Pro Dark mode
However only inverted colors.
Pro Scale, rotate and fit
Pro Supports TOC-sidebar
Pro Switch tabs with keyboard shortcuts
Pro Continuous and multiple-page layouts
Pro Add highlights and text annotations
Pro DjVu support
Pro Fullscreen and presentation views
Pro PostScript support
Pro Custom background colors
It is available on any major computer OS.
Pro Deactivation of GUI elements
Pro Supports thumbnail preview
Pro Input forms are editable
Pro Extensible, customizable and scriptable
Being a Emacs plugin you can use elisp to customize, script and extend pdf-tools.
Pro Can treat multiple PDF's as one big PDF
Pro Nice search using Occur
Occur creates a list all lines matching a regexp or string in one or more pdfs and allows easy jumping between them. Really helpful when searching long documents like datasheets.
Pro Synctex support
Pro Easy installation
Although installing requires little more work than stand-alone readers, pdf-tools is very easily installed via Emacs 'list-packages' or even easier as a layer in Spacemacs
Pro Convenient default keyboard shortcuts
Uses emacs or vim-style navigation (via spacemacs/evil. Shortcut overview via transient state "SPC m .")
Pro Automatically exported notes
Notes can be exported automatically to and backlinked from an external org notes file using the org-noter or interleave package.
Con Deadly slow on complex pdf files
Con File information missing page size
Con No multiple mapping of commands
Having two key mappings to execute the moveUp command doesn't seem to be possible.
Con Configuration intended via GUI
There is no explicit documentation of configuration parameters used in qpdfview.conf and shortcuts.conf (those are the most important ones). However the files are editable conveniently, which is of value.
Con Only for power users
Handy only for people that want good notes/annotation management. Otherwise using any other pdf-reader is recommended.
Con Too cumbersome for quick reading or annotating
Although setting up pdf-tools is not too much work. For quick reading using some default pdf-viewer like evince/okular/zathura is recommended. Also, except for the auto-export feature (with org-noter/interleave package), other editors like e.g. pdf-XChange Editor (via wine), Okular or mupdf have even more powerful annotation features.