Sometimes, the text in column header and cells are sent to Adobe PDF printer as pure text(selectable and copiable) while printing, but sometimes as image(not selectable).

I don't know how exactly this goes since on the same printed page there could be both vector texts and image texts. One thing is for sure that the font and apperence of texts are relevant. I checked the source code of UIElement, there is more than one method to draw texts, which is decided by itself. Is there some option to keep the text pure vector while printing? Is GDI/GDIPlus option of the grid helps?