Better PDF-reader for Ubuntu called qpdfview
The default PDF-reader in Ubuntu 16.04 is very plain and non-configurable, but it is easy to replace it with a better alternative, such as qpdfview, which is much more configurable.
"qpdfview is a tabbed document viewer using Poppler, libspectre, DjVuLibre, CUPS and Qt, licensed under GPL version 2 or later."
Install qpdfview with this command:
sudo apt-get install qpdfview
To set qpdfview as default application for PDFs, right-click on a PDF-file, select "Properties" > "Open With", select "qpdfview and "Set as default".
In qpdfview you can configure a lot of things, for example changing the shortcuts for zooming in and out to "+" and "-", and "Fit to page size" to "z". You can do this under Edit > Settings > Shortcuts.