Hi NaturaAdmin,
Nice idea there. I can see why that would make things a lot clearer for your customers, especially when you're sending different documents from sales order. Having the file name match the form or document type would definitely tidy things up a bit. At the moment though, in MYOB AccountRight the file name of emailed forms is automatically generated using the transaction reference, and there isn't a setting available to customise that file name based on the form or document selected.
If you'd like, you can pop it onto our Ideas Board so the product team can take a look and other users can vote it up as well. The more interest it gets, the better chance it has of being considered for future updates.
Regards,
Sai