Built-in PDF viewer + ability to hook up MIDI signals for pedals to scroll up/down on PDF scores.
I don't print out my scores -- instead just display them in a PDF viewer on my Pianoteq computer (dedicated Linux computer) -- so it's a huge hassle to stop playing in order to scroll up/down.
I've tried looking for Linux MIDI intercept software to try to hack this but haven't been successful.
Are you sure that MIDI signals aren't available to other applications at the same time? I'd wonder if ALSA MIDI isn't a bus and Pianoteque just reading the signals coming by (as opposed to the complete overtaking of the audio interface it you use the "direct" methods).
Of course it's in theory possible.
It's just nobody has programs to do this generically -- e.g. trap for MIDI signals to convert to keyboard macro strokes.
I just found VirtMus? https://sourceforge.net/projects/virtmus/ & http://virtmus.com/
There's even a guide on how to on convert an old mouse to a footpedal for switching pages ;-) http://virtmus.com/FootSwitch/index.html and a number of commercial solutions to generate keyswitches to do this. Using this info, you might also be able to use a pdf reader.
VirtMus seems to be written in Java, is also available for Mac and Windows, and is free; but latest development is from 2015. The Windows version worked on my W10;