- (NSSize)pixelSize
{
    CGImageRef CGImage = [self CGImageForProposedRect:nil context:nil hints:nil];
    NSBitmapImageRep *bmp = [[NSBitmapImageRep alloc] initWithCGImage:CGImage];
    return NSMakeSize(bmp.pixelsWide, bmp.pixelsHigh);
}


 NSColor *color = [NSColor redColor];
NSPDFImageRep* rep = self.representations.lastObject;
return [NSImage imageWithSize:self.pixelSize flipped:NO drawingHandler:^BOOL (NSRect dstRect)
        {

            [[NSGraphicsContext currentContext] saveGraphicsState];
            CGFloat lineWidth = 1.;
            NSBezierPath *strokePath = [NSBezierPath bezierPathWithOvalInRect:NSInsetRect(dstRect, lineWidth/2., lineWidth/2.)];
            [[NSColor whiteColor] set];
            [strokePath setLineWidth:lineWidth];
            [strokePath fill];

            [color set];
            [rep drawInRect:dstRect fromRect:NSZeroRect operation:NSCompositeSourceIn fraction:1 respectFlipped:YES hints:@{NSImageHintInterpolation: @(NSImageInterpolationHigh)}];

            [color set];
            [strokePath stroke];
            [[NSGraphicsContext currentContext] restoreGraphicsState];

    return YES;
}];