When I wanted a PDF reader, I simply went to the aps serch tab (bottom left) typed in "PDF Viewer" and the standard Adobe type icon appeared in the list... That was placed on the shelf for further use...
Whether or not that needs to be called up when reading a PDF, I'm uncertain... But I have a number of shuch documents stored in Google cloud and all I ever do is double click a file and it opens...
Once set up, it's also easy to print PDFs, using the cloud print process...
My biggest PDF file, is a user manual for a Galaxy Tab 3 ~ at 263 pages...
Hope that helps...
If you need any more assistance, please come back and ask... I will help if I can...