Use CopyForm to remove any unwanted pages. CopyForm takes two parameters a first page and a last page. You can call CopyFrom multiple times to add what pages you want. Something like this:

toolkit.CopyForm(1, 4);

You can also use MergeFile in a similar fashion.

CopyForm Documentation
MergeFile Documentation

Attached is an example and input PDF file that removes page number three from the output.

More Toolkit sample code at