In HandiTax you have the option to add password protection when exporting to tax returns to PDF, to do this, please follow the below steps:
Log into HandiTax.
Select the client and open the tax return.
Open the report preview window by selecting one of the report types e.g. View ATO Copy.
Click on File and then choose Export to PDF.
Select Password Protected.
Enter the password in the Open field.
Ensure Save is ticked and then click Generate.