Password protect a workbook created and emailed by a macro?

I have created a macro which dynamically creates a workbook, emails it, and
then creates another workbook with different information, emails it, etc. It
is generating individualized workbooks by going down a list. What I want to
do is to PASSWORD protect the workbook before it is emailed. I have tried
it, and so far it protects the workbook, but without adding the password.
The people I am sending this to enter information, and send it back, so I
really don't want them unprotecting the sheet and messing it up (like they
have been doing). Is there any way I can make the macro plug in the password
automatically?