Any kind of document in Google Drive can be accessed either
- by anyone with a link to the document
- by a specific set of users
- (for Apps domains) by the users of the domain
None of this is contingent on the acceptance of a license. To make your license work for real, you indeed need a web app (on the Apps Script platform) that would require the user to log in, and then edit the document by adding the user to the list of viewers of that document (i.e., item 2 above).
A cheap alternative is to only show the link to a document after the user accepts the terms. This can be done easily with a Google form: here is an example. The obvious drawback is that nothing stops the user who accepted the terms from copying the URL and sending it to others, or posting it on the web, etc. Those who follow that URL will get to the document directly.