Yes, you can attach files of content from other content structure via File Manager.
For example, suppose you have the following content structure with ID=30 and you have attached a file in its content.
If you want to use this content's files in
file(from File manager) in another content structure, create an extension field with
file(from File manager) type on content structure which you want to attach the file and configure as follows:
In this case, the number 30 should correspond to the content structure ID from which you want to attach the file from.
How to use
Once you have set the parameter in the previous step, you can attach the file through the File Manager in the content edit page.
Note that files from other content structures can only be read or attached. They cannot be updated or deleted.