Use this method to append one PDF to the end of another one.
Individual pages from one PDF can be drawn into another using
the AddImageDoc method.
If you are inserting a number of pages it is much faster to use
the Append method than to draw pages individually. It also has the
advantage of maintaining other information such as bookmarks.
If you are inserting pages that contain form fields, you may want to call
to avoid sharing fields across pages.
setting determines whether duplicate and redundant objects are
eliminated. The SaveOptions.Preflight
setting determines whether objects in the destination document are
validated before this operation is performed.
Unless the document and the pages are big in terms of memory use
and have many common objects, it is faster to disable
SaveOptions.Refactor and SaveOptions.Preflight for adding the pages
and enable them for saving the document.