How to read data files included in the app

Question

For my program I have to include huge index and data files in the program bundle. Because it is an universal app, I have included these files in a folder named \"Data\" with

Answer 1

After Romasz has brought me to the right path, I can see the problem is quite different there. My data files were involved in the correct place in the project, but Visual Studio does not bind all what you want. In my project I need large data files to be firmly integrated into the program. These are between 13 KB and 41 MB in size and have file types .idx and .dat. These names are part of the problem.

What I know so far:

I may add .txt files with seemingly arbitrary size. Tested with 41 MB - no problem. The same file with changed file type .idx is not added. The file is simply not included in the compiled project. No error message. Of course I can rename the .idx files to another file type (tested with .id), but I want to know why idx files are treated differently. And why I got no error indication.