How to create an attachment for a network shared file?

I would like to put the attachments in my common document storage and give the link as an attachment on the related documents for sending approval. Ex. I used to send PO documents for approval with attachment of quote and some addition information. Since this is required only at the time of approval, a URL link to the document will be good enough. If anybody has idea, please post.

I have tried the link as below;

file:///\\server_name\folder_name\file.ext

Thanks

Shanthi