As per your Error Message, this file is not an AxCrypt file format. Do you rename the file name?
Please rename the file name and try to open the same.
We have a feature called Try Broken File. You can able to decrypt the corrupted/damaged AxCrypt encrypted files by navigating the menu File | Options | enable Debug from the AxCrypt app.
Now you can able to see the Debug the menu in the AxCrypt app. From the debug menu you have to select Try Broken File.
Now you will be prompted for file selection. Select the corrupted encrypted file and then AxCrypt will try to decrypt the file. If successfully decrypted, then you are able to see the decrypted file in the location. Otherwise sorry to say, AxCrypt can’t decrypt that file.
still, if you are asking any Queries, please write to Support@axcrypt.net. we are happy to help you.