How can saveAs a PDDoc to image file?

My code process save PDDoc to Image:

PDDoc NewDoc = PDDocCreate ();

ASPathName imagepath ="E:\\Acrobat 10 SDK\\TestData\\Image.png"

imagepath = ASFileSysCreatePathName(NULL, ASAtomFromString("Cstring"),  str, 0);

AVDocOpenFromPDDoc(NewDoc, NULL);

PDDocSave(NewDoc, PDSaveFull | PDSaveLinearized, imagepath, NULL, NULL, NULL);

But result Image.png error can't  open.

How can saveAs a PDDoc to image file?

Thanks all.