Merge layers in pdf printed from AutoCAD

I create a .net automation application to print to pdf with layers. There are more 30+ layers in the drawing, I like to have the layer information in the pdf file but like to merge them to a couple: e.g.
PDF Layer 1 show AutoCAD Layer A1, A2, A3, ...,
PDF Layer 2 show AutoCAD Layer B1, B2, B3, ...,
PDF Layer 3 show AutoCAD Layer C1, C2, C3, ...,
...
I think there will be 3 solution here:
a) merge them at the time of AutoCAD printing
b) merge layer in pdf
c) create bookmark in pdf
any one of them will solve my problem. I have used iTestSharp to generate PDF file, merge PDF files but cannot find a solution for this. How I can do it programmically?

Thank you so much and Happy New Year
Wes

Wes