Google Drive — Right-click the file → Share → set to Anyone with the link (Viewer) → copy the link. The app converts it to a direct-download URL automatically. Note: files shared only with specific people or requiring sign-in cannot be downloaded this way.
Dropbox — Click Share on the file and copy the link. Change ?dl=0 to ?dl=1 (the app does this automatically).
OneDrive — Click Share → Copy link (set to Anyone). Paste the share URL here.
GitHub — Open the file → click Raw and copy the URL. Or paste a normal GitHub file URL; the app converts it.
Any direct URL — Any publicly accessible URL ending in .dxf works. If the server blocks cross-origin requests the app retries through a CORS proxy automatically.