Defines the mappings for substituting non-embedded fonts when rendering text.
Initializes a new PDFFontSubstitution object.
Gets the font mappings dictionary.
The dictionary is used to specify font data streams for fonts that are not embedded in the PDF file.
The string key in the dictionary must correspond to a font name (including the start /) in the PDF file. If that font is not embedded, the library will use the corresponding font stream to render the text.
The value /Default maps any non embedded font in the PDF file to a default font stream.
This method supports the internal library infrastructure and should not be used by external client code.