Restrict to move/drag the pdf annotation within PDF Page boundary

Question

I am loading one PDF on PDF view using the PDF kit library. I added one custome view (same like PDF Annotation) on pdf view, and I am allowing users to move/drag that custom view on pdf view(within pdf view/container view) using UIPanGestureRecognizer. Here is a gif,

If you see this gif, there is one problem. That custom view is going outside of the pdf page. I want to restrict it. The custom view should move/drag within the pdf page only. How I can fix this? Is there a solution for it?

Here is the link sample project and all code - https://drive.google.com/file/d/1Ilhd8gp4AAxB_Q9G9swFbe4KQUHbpyGs/view?usp=sharing

Here is some code sample from project,

override func didMoveToSuperview() {
        addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(pan)))
    }

@objc func pan(_ gesture: UIPanGestureRecognizer) {
    translate(gesture.translation(in: self))
    gesture.setTranslation(.zero, in: self)
    setNeedsDisplay()
    print("Frames after moving : \(frame)")
}

and code used as an extension

extension  CGPoint {
    static func +(lhs: CGPoint, rhs: CGPoint) -> CGPoint {
        .init(x: lhs.x + rhs.x, y: lhs.y + rhs.y)
    }
    static func +=(lhs: inout CGPoint, rhs: CGPoint) {
        lhs.x += rhs.x
        lhs.y += rhs.y
    }
}
extension UIView {
    func translate(_ translation: CGPoint) {
        let destination = center + translation
        let minX = frame.width/2
        let minY = frame.height/2
        let maxX = superview!.frame.width-minX
        let maxY = superview!.frame.height-minY
        center = CGPoint(
            x: min(maxX, max(minX, destination.x)),
            y: min(maxY ,max(minY, destination.y)))
    }
}

Code - Get PDF Page Height and Width

 let page = pdfDocument.page(at: 0)
 let pageRect = page?.bounds(for: .mediaBox)

 print("pdf page width =", (pageRect?.size.width)!, "pdf page height =", (pageRect?.size.height)!)