Hi,

You could create a page and insert the bizform webpart into this page (instead of page with login form). Then you can set redirect URL in the definition of appropriate bizform: 'Redirect to URL' field of 'CMS Desk-> Tools-> BizForms-> General' tab. This Redirect to URL could look like ~/download.aspx?visibility=true. To decide which transformation should be used on a download page you can use this query parameter. You could use it in query parameter macro, i.e. {%visibility%} in this case.

This is only simple example. The user could access the download page using http://domain.com/download.aspx?visibility=true directly instead of using http://domain.com/download.aspx and he would not be forced to insert data into the bizform.

You could insert a guid field into bizform of Unique identifier (GUID) type. This field would not be visible in public form. This GUID could be used as "download availability decider".The bizform return url could look like:
~/download.aspx?visibility={%GuidColumnName%}
Now to decide which transformation could be used you could create a custom macro and in this macro check if record with the GUID exists in the biz form table.

I hope the description makes sense.

Best regards,
Ivana Tomanickova