Adobe Digital Editions 4.5 – E_ADEPT_DOCUMENT_TYPE_UNKNOWN error with Google Play Books

I am contacting you regarding a persistent technical issue with Adobe Digital Editions (ADE) 4.5 on Windows 11, which prevents me from downloading and reading a legally purchased eBook from Google Play Books.

The error message displayed by ADE is:

“Unable to download. Error getting License. License Server Communication Problem: E_ADEPT_DOCUMENT_TYPE_UNKNOWN”

1. Description of the problem

I purchased an eBook through Google Play Books. The book remains fully accessible and readable in my Google Play Books library using Google Chrome.

However, whenever I attempt to export the book in either EPUB or PDF format, Google Play Books generates an ACSM file which Adobe Digital Editions fails to process.

The same error occurs with both export formats.

2. Troubleshooting already performed

Following detailed instructions from Google Support, I completed the following procedures:

1. Verified that the computer's date and time are correct.
2. Confirmed that the internet connection is functioning normally.
3. Removed the unsuccessful book entry from the ADE library and downloaded a fresh ACSM file from Google Play Books.
4. Completely uninstalled Adobe Digital Editions and reinstalled version 4.5 using the official Adobe installer.
5. Restarted Windows 11 after installation.
6. Verified that Adobe Acrobat Reader is installed and fully updated.
7. Checked ADE authorization. The application confirms: “The computer is already authorized.”
8. Tested access to the Adobe activation server at http://adeactivate.adobe.com/. The server responded with HTTP 404, rather than the “Welcome to Digital Editions” message mentioned in Google's troubleshooting instructions.

Despite these actions, the original error remains unchanged.

3. Google Support investigation

I contacted Google Play Support and provided the exact purchase order details.

After reviewing the case and escalating it to their technical specialists, Google informed me that their troubleshooting procedures had not resolved the problem and explicitly recommended contacting Adobe for further assistance.

I have therefore exhausted the troubleshooting steps recommended by Google.

4. Request for technical assistance

I would appreciate your assistance in determining:

1. What specifically causes the E_ADEPT_DOCUMENT_TYPE_UNKNOWN error when ADE processes ACSM files generated by Google Play Books?
2. Whether this error indicates an incompatibility between Google's ACSM export mechanism and Adobe's DRM licensing infrastructure.
3. Whether there is a known issue affecting Adobe Digital Editions 4.5 and Google Play Books.
4. Whether a corrective procedure, patch, or officially supported workaround is available.

Please note that I am not experiencing a general Windows or internet connectivity problem, and Adobe Digital Editions is already authorized.

I would particularly appreciate a technical diagnosis rather than another standard reinstall-and-reauthorize procedure, which has already been completed without success.

If necessary, I can provide screenshots of the error, details of the Google Play purchase, and the correspondence exchanged with Google Support.

Thank you for your attention. I look forward to your technical assessment and recommendations.