Hello David,
You can’t.
For the same reason that if you zip a file to a zip archive, it ends with .zip and if it was for example a Word document, now you can’t open it in Word directly.
Word-files are Word files and are identified in Windows by their extension, .docx.
Excel-files are Excel files and are identified in Windows by their extension, .xlsx.
PDF-files are PDF files and are identified in Windows by their extension, .pdf.
Zip-files are zip files and are identified in Windows by their extension, zip.
AxCrypt-files are AxCrypt files and are identified in Windows by their extension, .axx.
Event though an AxCrypt-file may contain a word file or an excel-file or even a zip-file, neither ‘native’ application can interpret and decrypt the AxCrypt-file directly to get at the contents. AxCrypt is in this sense a ‘container’ file format, similar to .zip in many ways.
That’s why AxCrypt handles this process for your when you double-click an AxCrypt file.
Then AxCrypt decrypts the original file with the original extension, and then asks Windows to open the file with whatever application is registered for the extension, for example Office Word for a word file ending with .docx .