If you come across the message "File does not exist" when trying to open a file (e.g. from the files app), it's likely that the file is stored in a different location/device, and or the device doesn't have access to the file.
Please take the following points into consideration:
The Files app allows you to manage files like DWGs across 2 locations.
Cloud storage service (e.g. iCloud Drive):
These files are synced through your Cloud storage. For example, if you use iCloud, you can also try to access your files directly in ARES Touch under "My files in the cloud" -> "iCloud". Note that you may need to setup the Cloud storage service in different devices in order to be able to access the files/storage content.
Files stored locally/in your device:
These files are all files that you can see and manage directly in ARES Touch under "My local files" -> "Documents".
For both storage locations, a directory "ARES Touch" should be available under "Files".