@meike.bornand,
Thanks for posting your inquiry. The evaluation watermark appears when license is not initialized, therefore, please double check that your application has access to the location where license file is placed and also, the current user with whom the application is being accessed has permissions to that location/path. The following points might also be helpful for you regarding the licensing issue:
- Make sure the input documents do not already have the evaluation message.
- Check if your code does not catch an exception thrown by GroupDocs.Viewer licensing code.
- Clear GroupDocs.Viewer’s cache folder and try again.
In case the issue persists, please share with us your license file via private message (see how to send private message). Furthermore, please share the system/environment details (i.e. OS details, .NET framework version) of your production server as well as the development server. We shall be looking forward to hearing from you.