Adding pages to an Encoder object implicitly groups an "encoding session" and the method is explicitly closes the session.

When EncoderParams.DictionaryUsage Property is true, all the pages in an encoding session shares a dictionary. And by closing an encoding session, it generates a dictionary for the pages in the session and finalizes the structure for the pages. If EncoderParams.DictionaryUsage Property is false, the method does nothing.

There are several situations, on which the method is called implicitly. If EncoderParams.DictionaryUsage Property os true and NumPagesShareDict Property is not 0, Encoder.AddPage Method/Encoder.AddPages Method calls the method on each NumPagesShareDict pages. The other is GetEncodedDocument Method. It internally calls the method if needed.

Target Platforms: Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows Server 2008 family

Reference

Encoder Class
Encoder Members