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How to render a PDF to an image

Paul Hudson       @twostraws

iOS has built-in APIs for drawing PDFs, which means it's relatively straight forward to render a PDF to an image. I say "relatively" because there's still some boilerplate you need to worry about: figuring out the document size, filling the background in a solid color to avoid transparency, and flipping the rendering so that the PDF draws the right way up.

To make things easy for you, here's a pre-made method you can use that takes a URL to a PDF and returns either a rendered image or nil if it failed. To call it you should pull out the URL to a resource in your bundle or another local PDF file.

func drawPDFfromURL(url: URL) -> UIImage? {
    guard let document = CGPDFDocument(url as CFURL) else { return nil }
    guard let page = document.page(at: 1) else { return nil }

    let pageRect = page.getBoxRect(.mediaBox)
    let renderer = UIGraphicsImageRenderer(size: pageRect.size)
    let img = renderer.image { ctx in
        UIColor.white.set()
        ctx.fill(pageRect)

        ctx.cgContext.translateBy(x: 0.0, y: pageRect.size.height)
        ctx.cgContext.scaleBy(x: 1.0, y: -1.0)

        ctx.cgContext.drawPDFPage(page)
    }

    return img
}

Available from iOS 3.0

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