I have to read the text content from an .txt file, this file is located in app installed folder, in a subfolder, according to Microsoft docs, I am doing it like
.txt
I think you need to use:
string txtFileName = @".\myfolder\myfile.txt";
The dot in the filename represents the current folder. In you want to specify using relative paths, then @"\myfolder\myfile.txt" is not correct.
@"\myfolder\myfile.txt"