How to attach files to node instead of uploading?
Try the Attachment Links module

The Attachment Links module provides permanent links to files attached to a node. A single, easy-to-remember URL can be used to retrieve the preferred (canonical) or newest version of a file regardless of how many versions of that file have been attached to a node.
Typically, users will want to create a &quot;File&quot; content type and enable the Attachment Links module for that content type. Each &quot;File&quot; node should refer to a single file: &quot;Handbook,&quot; &quot;Company logo,&quot; &quot;Team roster,&quot; etc. Though each node could contain multiple versions of the file, Attachment Link provides permanent link to access the preferred or newest versions.

It seems you can also use the IMCE for FileField module to get the uploaded files from other content type. check this answer  posted by me.