It seems you are moving encrypted files out of your BoxCryptor _folder_ (that is mapped to your BoxCryptor virtual _drive_).
Then you are moving those files in encrypted form, and get garbage when trying to open.
Instead, you should be moving encrypted files out of your BoxCryptor virtual _drive_.
In that case files are decrypted while being moved out of the virtual _drive_.
There is one exception (probably not relevant for your problem):
If you have multiple BoxCrytor _folders_, each mapped to a BoxCrytor _drive_
while using THE SAME KEY for encryption for these folders, you can/should move or copy encrypted files from one BoxCrytor _folder_ to another BoxCrytor _folder_.
After all, that is the concept BoxCryptor is based on; it allows e.g. DropBox or GoogleDrive to (cross-site) sync files from one BoxCryptor _folder_ to another BoxCrytor _folder_ in encrypted form.
You should open these files from the respective BoxCrytor virtual _drives_.