Hello Henry Liao,
The error message indicates that the file simply is not an AxCrypt file – it checks the first 16 bytes for a unique value.
Most often, this error occurs because the file is not produced by AxCrypt, but rather a different kind of file accidentally renamed to end with .axx.
Another scenario is that it is a left-over after a previous decryption was interrupted at the stage where the original is overwritten. The most common reason for this happening is that the file was damaged because of early removal of a USB drive, or a disconnected network drive.
If the file is actually damaged to this extent, no, it can’t be fixed. The data is just not there to decrypt it.
But we have a feature called Check File. You can able to decrypt the corrupted AxCrypt encrypted files by navigating the menu File | Options | enable Debug from the AxCrypt app.
Also we can generate a summary of file structure, to see whether the file was encrypted with AxCrypt or not.
For the summary, you have to use the debug menu and then select the Check File menu option(Debug | Check File). Now you will be prompted to choose the files. Choose the AxCrypt encrypted file. Then AxCrypt will generate a summary of file structure.
Just take a screenshot of the summary and send to us, to investigate the file status.