问如何使用PDFKit在位置中添加字符的边框？

EN

class WatermarkPage: PDFPage {

    // 3. Override PDFPage custom draw
    /// - Tag: OverrideDraw


    override func draw(with box: PDFDisplayBox, to context: CGContext) {

        // Holding the char positon
        var rect = CGRect()

        // Draw original content
        super.draw(with: box, to: context)

        // Draw rotated overlay string
        UIGraphicsPushContext(context)
        context.saveGState()

        if let doc = document, let page = doc.page(at: 0){
            rect = page.characterBounds(at: 1)
        }

        let pageBounds = self.bounds(for: box)
        context.translateBy(x: 0.0, y: pageBounds.size.height)
        context.scaleBy(x: 1.0, y: -1.0)
        context.rotate(by: CGFloat.pi / 4.0)

        let string: NSString = "U s e r   3 1 4 1 5 9"
        let attributes = [
            NSAttributedStringKey.foregroundColor: UIColor(red: 0.5, green: 0.5, blue: 0.5, alpha: 0.5),
            NSAttributedStringKey.font: UIFont.boldSystemFont(ofSize: 64)
        ]

        string.draw(at: CGPoint(x:250, y:40), withAttributes: attributes)
        context.fill(rect)
        context.restoreGState()
        UIGraphicsPopContext()

    }


}