Ahh, just brainstorming here:
If you want to block a page from any user seeing it I don't know how you can accomplish that, hence the necessity of authentication. However, if you are willing to try something different why not just collect their name and e-mail address (and what ever
other data you want to "collect") and then send a response e-mail with the attached document. If there is a choice of documents, just slap on a drop down list or radio button list with the choices. Then do some logic to send the appropriate attachment.
The thing about gathering "different information concerning users than the simple info managed by user profile" is you are either going to save that information in the database (which is not necessarily a bad thing), or you are going to somehow
get at that information and do something with it (there is a circular argument here: because getting the information and storing it somewhere necessitates saving in a database, and if you are going to do that then why not just save it in Orchard).
Another thing you might do (it stores info in the database) is use Orchard.CustomForms. You can create a form to save information about the user and then create a rule (if you want) to shoot them or yourself (or both) an e-mail with the information. The
information is accessible in the Admin Dashboard>Forms. The problem is how do you then serve an attachment to the e-mail (is this possible with Rules/CustomForms?).
Again, just brainstorming. Please someone chime in if there is another way to handle what @csadnt wants.