Thank you for the interest in RadPdfViewer.
1. Custom filter is used as soon as it is registered. You don't need to reload the document source if the registration happens before initializing the control (before InitializeComponents or in the static constructor).
2. Currently changing the color space is not respected. We will consider respecting it but I cannot give you any time frame when it will be implemented. At this point the returned data should match the color space specified by the PdfObject.ColorSpace property.
Hope this answers your questions.
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