PSPDFTouchForwardingView.swift

import UIKit

// This class allows the "presentedController" to receive touches
// https://pspdfkit.com/blog/2015/presentation-controllers/
class PSPDFTouchForwardingView: UIView {
    
    var passthroughViews: [UIView] = []
    
    override func hitTest(point: CGPoint, withEvent event: UIEvent?) -> UIView? {
        guard let hitView = super.hitTest(point, withEvent: event) else { return nil }
        guard hitView == self else { return hitView }
        
        for passthroughView in passthroughViews {
            let point = convertPoint(point, toView: passthroughView)
            if let passthroughHitView = passthroughView.hitTest(point, withEvent: event) {
                return passthroughHitView
            }
        }
        
        return self
    }
}

Thanks for that!
Swift syntax is a bit outdated though, here is the up-to-date 5 version as of October 2021.

class PSPDFTouchForwardingView: UIView {

    var passthroughViews: [UIView] = []

    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        guard let hitView = super.hitTest(point, with: event) else {
            return nil
        }
        guard hitView == self else {
            return hitView
        }

        for passthroughView in passthroughViews {
            let point = convert(point, to: passthroughView)

            if let passthroughHitView = passthroughView.hitTest(point, with: event) {
                return passthroughHitView
            }
        }

        return self
    }
}