If you want to delete a torrent file from your device using the 
Torrent Pro app, you can follow these simple steps:
Tap and hold on the torrent file that you want to delete.
Tap on the ‘trash’ icon in the menu that appears.
A deletion dialog will pop up. Make sure to select the ‘Delete with downloaded files’ option.
Tap on ‘Confirm’ to proceed.
By doing this, you will remove the torrent file from the app and your device. It will not remain in your file manager. Here is an image of how it looks like in Torrent Pro: