A repository server that makes stored copies of Web-accessible documents available at times when the documents themselves are inaccessible via the Web, because the server the document is located on is unavailable, because the server has removed or renamed the document, or because the server has replaced the version of which the stored copy is a copy with a different version. A client of the repository server may register a document in the repository server. The repository server makes a copy of the registered document and returns a repository URL for the copy to the client. The repository URL may be used to fetch the copy from the repository URL. Registration further relates the stored copy to its document URL, to an identifier for the stored copy, to a fingerprint that is a condensed representation of the stored copy's content and to a set of stored copies having similar content.