pdf首页封面的抓取

1. - (UIImage *)p_w_picpathFromPDFWithDocumentRef:(CGPDFDocumentRef)documentRef {
2.     CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1);
3.     CGRect pageRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox);
4.  
5.     UIGraphicsBeginImageContext(pageRect.size);
6.     CGContextRef context = UIGraphicsGetCurrentContext();
7.     CGContextTranslateCTM(context, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect));
8.     CGContextScaleCTM(context, 1, -1);  
9.     CGContextTranslateCTM(context, -(pageRect.origin.x), -(pageRect.origin.y));
10.     CGContextDrawPDFPage(context, pageRef);
11.  
12.     UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
13.     UIGraphicsEndImageContext();
14.     return finalImage;
15. }