XObject
An external object (commonly called an XObject) is a graphics object whose contents are defined by a self-
contained stream, separate from the content stream in which it is used. There are three types of external
objects:
An image XObject PDF::XObject::Image represents a sampled visual image such as a photograph.
A form XObject PDF::Object::XObject::Form is a self-contained description of an arbitrary sequence of graphics objects.
A PostScript XObject PDF::Object::PS contains a fragment of code expressed in the PostScript page description language. PostScript XObjects should not be used.