Attachment names are unique for a document (or its version). If you try to upload an attachment that has the same name as some already existing attachment of the particular document, the new attachment gets a number in the -(1) format attached to its name.

 

This happens for the attachments to be accessible via friendly URLs in the following format:

 

 

Page url: http://devnet.kentico.com/docs/5_5r2/devguide/index.html?attachment_names.htm