The URL field in the License Properties dialog specifies a URL that must be accessible in order for the rights to be granted. This allows you to control the lifetime of a file protection license remotely.
For example, suppose you protect a file called BID.DGN and you create an Everyone license in this file with the specified URL:
Then you send the protected BID.DGN to a contractor. When the contractor tries to open his copy of BID.DGN, his MicroStation will first check if he can access http://www.mycompany.com/bidisvalid. If so, it opens the file. If not, it refuses. You can therefore cancel the contractor's right to access his copy of BID.DGN by removing the "bidisvalid" document from your website.
Note that the URL must include the scheme. Currently, only "http://" and "https://" are supported.
I should mention that a determined user could circumvent the URL check. A user could also circumvent the expiry date check. Checks like these are intended to communicate your wishes to people that you trust. They are not meant to control the behavior of adversaries or "bad guys." The only way to keep a bad guy from misusing your data is to deny him access to it. The only sure way deny access to a protected file is to create a license based on a strong password or, better yet, a digital certificate. That way, only the intended recipient will be able to open the protected file in the first place.