Checks if the page blending color space has been defined in the PDF document.
You must set the required blending color space and the required luminosity softmask blending color.
When Adobe Acrobat interprets transparent objects and attempts to create a preview of the flattened artwork, it needs to do so using a single color space for all the items involved in the transparency group. This color space is called the blending color space.
The page blending color space is the blending color space assigned to a page; it is used when individual artwork does not have a blending color space.
The blending color space for soft masks (masks with soft transitions) is called the luminosity softmask blending color space. It is usually gray.