A file specification represents the name and location of a file
and optionally may also include references to embedded data.
The crucial properties of this class are Uri and EmbeddedFile.
All other methods and properties are organized around backwards
compatibility with obsolete entries so you are unlikely to need
them when constructing new documents..
If you have an old PDF which contains obsolete entries, the
Rationalize method will attempt to make the entries compliant. So
again you should only need the Rationalize method and the Uri and