Estou preso na análise de um arquivo PDF. Por favor, me guie como fazer isso.

Arquivo de cabeçalho.

//PDFViewer.h
@interface PDFViewer : UIView 
{
 CGPDFDocumentRef pdf;
}

-(void)drawInContext:(CGContextRef)context;

@end

Arquivo de implementação

//PDFViewer.m
@implementation PDFViewer


- (id)initWithFrame:(CGRect)frame 
{

 if ((self = [super initWithFrame:frame])) 
 {
        // Initialization code
  if(self != nil)
  {
   CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), CFSTR("WR1MayJun1S08.pdf"), NULL, NULL);
   pdf = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
   CFRelease(pdfURL);
  }
    }
    return self;
}


-(void)drawInContext:(CGContextRef)context
{
 // PDF page drawing expects a Lower-Left coordinate system, so we flip the coordinate system
 // before we start drawing.
 CGContextTranslateCTM(context, 0.0, self.bounds.size.height);
 CGContextScaleCTM(context, 1.0, -1.0);

 // Grab the first PDF page
 CGPDFPageRef page = CGPDFDocumentGetPage(pdf, 1);
 // We're about to modify the context CTM to draw the PDF page where we want it, so save the graphics state in case we want to do more drawing
 CGContextSaveGState(context);
 // CGPDFPageGetDrawingTransform provides an easy way to get the transform for a PDF page. It will scale down to fit, including any
 // base rotations necessary to display the PDF page correctly. 
 CGAffineTransform pdfTransform = CGPDFPageGetDrawingTransform(page, kCGPDFCropBox, self.bounds, 0, true);
 // And apply the transform.
 CGContextConcatCTM(context, pdfTransform);
 // Finally, we draw the page and restore the graphics state for further manipulations!
 CGContextDrawPDFPage(context, page);
 CGContextRestoreGState(context);
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
}
*/

- (void)dealloc 
{
    CGPDFDocumentRelease(pdf);
 [super dealloc];
}


@end

Agora estou adicionando esta classe (PDFViewer.h) ao meu MainViewController.

//MainViewController.m

CGRect frame = CGRectMake(0, 200, 300, 500);

PDFViewer *pdfViewer = [[PDFViewer alloc] initWithFrame:frame];
CGContextRef context = UIGraphicsGetCurrentContext();
[pdfViewer drawInContext:context];
[self.view addSubview:pdfViewer];

Não mostra nada. Eu recebo os seguintes erros / avisos:

local MultiView[2850] <Error>: CGContextTranslateCTM: invalid context
local MultiView[2850] <Error>: CGContextScaleCTM: invalid context
local MultiView[2850] <Error>: CGContextSaveGState: invalid context
local MultiView[2850] <Error>: CGContextConcatCTM: invalid context
local MultiView[2850] <Error>: CGContextRestoreGState: invalid context

o que estou perdendo?

Saudações.