The identifier appears to be a unique file hash (likely a truncated MD5 or SHA fingerprint) or a temporary session ID used by a web server to facilitate a "Datei herunterladen" (Download file) request.
: Do not let the browser "Open" it automatically; save it to your "Downloads" folder first. Datei herunterladen 68C23E0C8840E0C6EF14DADEB2B...
: German administrative sites (ELSTER, AusweisApp) often use long alphanumeric strings for secure document retrieval. The identifier appears to be a unique file
Could you provide the or the website where you saw this so I can help you identify exactly what the file is? Datei herunterladen 68C23E0C8840E0C6EF14DADEB2B...