If you know where the file came from, you can try to include the .pdf extension if it is missing, which may allow your device to recognize and open it.
Invoices, receipts, or bank statements often use these numeric strings as unique transaction IDs. Download file(1656836883) pdf
A "Print to PDF" or "Export" action from a website where the system didn't assign a descriptive name. If you know where the file came from,