In simple words, create/upload a pdf to https://acrobat.adobe.com/ under the "Adobe Scan" folder. Now go to the app and you won't find it. This seems to be a bug! Document from web are missing on the App.
Sorry for the delayed response.
We tried reproducing the issue on our end but things were working fine for both the uploading part and opening it on either platforms later.
You might once try to remove the keychains from your device and then try to re-login on to the application and check.
Thanks,
Souvik.