You should have a header file together with libMTRInfoBox.so.1.0.1.

First, you must add
INCLUDEPATH += /home/mtr/Programowanie/Projekty/MTRInfoBox
to the .pro file to make it possible to include a header file from /home/mtr/Programowanie/Projekty/MTRInfoBox.

Then, you should use the exact name of the header file in include directive, not "MTR::InfoBox". I don't know what is the header called but let's say its name is mtrinfobox.h:
Qt Code: 
  1. #include "mtrinfobox.h"
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