This method is provided for low level control over obsolete
entries contained in old PDF documents.
So in general you should be using the Rationalize method and the Uri property rather than this
A FileSpecification may hold multiple paths to a file.
Each path is specific to a platform such as Mac, Windows or
Unix. For further details see the Platform property.
This function allolws you to retrieve the path for the specified
If there is no matching path then null will be returned.