Managing Files and access

You'll need the http://drupal.org/project/cck and http://drupal.org/project/filefield modules. You create a content type at admin/content/types then add the field via the 'manage fields' tab on the content type edit form of the content time you created.

If you used the private upload module, then you could make the file available to guests by unchecking a tickbox after a month of keeping it private: http://drupal.org/project/private_upload However, the module has some important incompatibilities, and still looks fairly buggy.

What about this as a different approach:

create a new content type called newsletter.
If you want to do it nicely, you could use cck fields for date and description, and not have a body.

create a new node each time you have a new newsletter, and attach the new pdf file to the node.

Use one of the 'node access' modules to make the node initially only available to auth users.
To do this, these modules usually provide permission checkboxes in the node's create/edit page.

Use the Views module to make a listing of all attachments for the newsletter content type.
Only the users with permission to see the node will see the attachment in the Views list. Thus, your auth users will see all the attachments listed, whilst your anon users only see those files on nodes that have had their access permission changed to 'anon'.

Note that if you didn't want to use Views to build your attachment list (if you haven't used it, it can be quite complex to begin with), you could do a very simple list with menu items in a menu block. This would work because anon users are not shown menu items if they don't have permission for the node. The menu items can be created and managed from within each 'create/edit node' page, so you don't have to edit the block directly/manually.

So each month you just edit the last newsletter and tick the 'anon' box that the access module provides.
The attachment (or menu item) will automatically appear in the list for the anonymous user.

Now, obviously this does NOT involve making files private. So if a guest can guess the filename, then they'll be able to download the file by linking to it directly. For example, if you use the same format each month, such as sept09.pdf, it is easy for someone to guess that next month's is going to be named dec09.pdf. The way around this is to add a random string to the file name of each newsletter. Eg. dec09-s6h4a.pdf

BTW, the reason I think it is fairly pointless to try to make downloads like this private is that, if your resources are 'valuable' enough, there is nothing you can do to stop members downloading them and sharing them via another website or bittorrent anyway. It would be worth doing if there were no disadvantages, but personally I think that the current 'file privacy solutions' cause too many difficulties and restrictions to make it worthwhile.

The access module would have to be written expressly to integrate with the rules module.
It would state this on the project page. But I suspect you might be stuck with using this one:
http://drupal.org/project/content_access as it is probably the only one to do so.

Be aware that trying to automate this is not going to be an easy task.
You are better to start support issues in the rules and content access issue pages if you
encounter any difficulties; you are more likely to get help from the developers of the modules.

Personally, I don't see the point of automating it. If you're adding a new letter every month anyway,
it is no work to go edit the last one a tick the permissions checkbox; it's like 20 seconds. Weigh
that against spending 5-10 hours trying to get the rules module to work. Is it really worth it?

Use the content_access module, follow the tutorial at http://drupal.org/node/517674, and use "+ 31 days" instead of "+1 day". Set the original permissions of the content type to viewable by authenticated users then use the "grant permissions by role" content access rules action to change it to the anonymous role. It's somewhat confusing the first time you do it, but eventually it all makes sense.