Before a file can be added to the download library, the type of file has to be added to the download library settings.
The Download Library page text can be managed under Downloads Settings
File Types Allowed
Enter the extension for the type of file that will be offered in the download library. This is case sensitive so it would be best to add the file type in lower and upper cases. Each file type extension can be separated with a comma.
Save the Changes
Click on the button.