A single document can reside in multiple folders because folders contain pointers to documents rather than actual copies. Documents that are in a static folder can be added to another folder by copying the link from one folder to another.
Using the Copy to Folder function does not create a copy of the original document. For steps on copying documents, see Copying Pages and Documents in the Separation Workspace.
To copy a document from its current folder to another folder:
After copying, each folder contains a link to a single copy
of the document. If the document is modified in one location, the changes are reflected
in both locations.
Note:
You may not be able to manually add documents to all folders. For potential conditions preventing you from adding documents to a folder, see If You Cannot Add a Document to a Folder