Q: I need to be able to programmatically add PDF layers (which I
understand in back-end PDF terminology are called "optional context
groups" ?) of differing colours to specific pages within a PDF file.
The objective is to be able to view individual pages with their "true"
background colour effectively turned "on" or "off". Producing the
whole document in colour does NOT give a true rendition of the page
colour: it gives a graduated, paler or darker image. Using layers DOES
give a true background. I'm not sure I have explained this very well,
so I'll try to give an example: imagine a document which consists of
multiple pages of Black and White, Colour photos etc within it is, for
the sake of argument, one page with a yellow layer added to the
background with black text in the foreground; without effecting the
colour or black and white properties of any other page in the document
we wish to have the facility to view as/output as either a yellow
background page OR black and white.
I principally program in VB.Net (VS2005), although I am familiar with
VB6/VB scripting and can understand C# to a limited extent.
I would be grateful if you could confirm that the PDFNet SDK
(www.pdftron.com/net) has the necessary properties/methods to enable
this manipulation - and if an example code segment could be given all
the better 
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A: You can use PDFNet SDK to programmatically add and process PDF
layers (and OCG ). As a starting point you may want to take a look at
PDFLayers sample project (http://www.pdftron.com/net/
samplecode.html#PDFLayers).