Permission the user to only view the metadata tab and not view the document. Document class

The file data and metadata for a given object do not have separate permissions; it's not possible to allow users access to the metadata but not the file.

If you need to do this then you probably have to separate the data into two objects: one with the metadata that the user should be able to see, and one with the file that they should not.  You can then control the ACLs on the two objects individually to achieve what you want.