Hello Uwes,
Sorry for the inconvenience caused. Assuming you are using Adobe Reader on the Windows machine, please sign out and sign back in Adobe Reader using your current Adobe ID and password, reboot the machine and see if this brings any changes.
Make sure that you are using the same Adobe ID(email) to access the Document Cloud files from the system which you have used in the Android tablet.
Try accessing the files from the URL https://cloud.acrobat.com/recent on a browser like Chrome or Firefox or Safari and check for the files.
Would you mind sharing the screenshot of the error you are getting? To share the screenshot, refer to https://forums.adobe.com/docs/DOC-7043#jive_content_id_How_do_I_attach_a_screenshot
You may also refer to the Adobe article Manage and work with your files stored in Adobe Document Cloud
Let us know if it works out.
Thanks,
Anand Sri.
[Edited Response]