If you are currently, or plan to be, a use of the mobile application please endorse this enhancement request.
The mobile application currently supports adding receipts from the native photos app or images captured with the camera only. We are suggesting adding functionality to allow users to pull other document types (PDF, etc.) from the local device. Main use case, suppliers that provide receipts via email that could be saved to the device and then uploaded as a receipt.
LINK: Add support for PDF attachments (from local device) to Mobile Application
Thanks!