Firstly I would recommend the following post to read:
Regarding the question
it means that Acrobat did create a copy of the file outside of Cryptomator’s control.
If your phone is rooted you can check the directory /data/user/0/org.cryptomator/cache/decrypted/ after locking the vault but as stated in the post above, this is only possible on rooted phones because otherwise the sandbox model of Android does not allow it for very good reason.