Preload UIImage for super-smooth interaction. especially great if you use JPGs, which otherwise produce a noticeable lag on the main thread.

UIImage+PSPDFKitAdditions.m

- (UIImage *)pspdf_preloadedImage {
    CGImageRef image = self.CGImage;
    
    // make a bitmap context of a suitable size to draw to, forcing decode
    size_t width = CGImageGetWidth(image);
    size_t height = CGImageGetHeight(image);
    
    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef imageContext =  CGBitmapContextCreate(NULL, width, height, 8, width*4, colourSpace,
                                                       kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);
    CGColorSpaceRelease(colourSpace);
    
    // draw the image to the context, release it
    CGContextDrawImage(imageContext, CGRectMake(0, 0, width, height), image);
    
    // now get an image ref from the context
    CGImageRef outputImage = CGBitmapContextCreateImage(imageContext);
    
    UIImage *cachedImage = [UIImage imageWithCGImage:outputImage];
    
    // clean up
    CGImageRelease(outputImage);
    CGContextRelease(imageContext);
    
    return cachedImage;
}

Pls don't forget to add old image orientation with:
let cachedImage = UIImage(cgImage: outputImage, scale: scale, orientation: imageOrientation)