TransparentBlt return false in some printer devices.

[molistok]

I am using the function TransparentBlt of CImage class and in a lot of printers the bitmaps are printed in transparency correctly. But in some printer devices TransparentBlt function return false (for example Adobe PDF 6.0) and therefore the bitmaps are not printed. What can be the problem? How I can know if the printer will print correctly the bitmaps?

This is my code:

void DrawTranspBm(CDC * pDC, const CRect* pRt, COLORREF crColour, HBITMAP hBitmap)
{
CImage img;
img.Attach(hBitmap);
BOOL bRet=img.TransparentBlt(pDC->GetSafeHdc(),*pRt,crColour);
}

Can any help me please?
Thanks.