for windows 10 mobile preview 10586.11 and a few builds before too, i have been able to print over wifi to my hp printer...
PDF documents are a pain - you have to have an app that allows you to do it -the adobe reader wants in app purchase to do that..
office lets you print over wifi... word and excel both tried.
I do know someone who had tried to use his epson printer and he was having an issue with it... i think he may have given up on it as he said it was not on the list of official supported printers by windows 10 mobile - the key here is mobile, as desktop obviously will support epson printers... but i think this is just a case of drivers...