I have a custom view that adds a WKWebView like this:

 override func awakeFromNib() {
    super.awakeFromNib()
    loadWebView()
}

func loadWebView() {
    pdfWebView = WKWebView(frame: .zero)

    pdfWebView.navigationDelegate = self
    pdfWebView.translatesAutoresizingMaskIntoConstraints = false
    pdfWebView.isHidden = true
    self.addSubview(pdfWebView)
    ... add constrains to self anchors - top, left, right, bottom
}

When loads finishes, I have this:

  func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.8, execute: {
        SVProgressHUD.dismiss()
        webView.isHidden = false
        webView.isOpaque = true
        webView.adjustInsets()
    })
}

I had to adjust the insets, because on iPhone X, sometimes the pdf sticked to the bottom, instead to the top.

extension WKWebView {
    func adjustInsets() {
        parentViewController?.automaticallyAdjustsScrollViewInsets = false
        scrollView.contentInset = .zero
        scrollView.scrollIndicatorInsets = .zero
        scrollView.contentOffset = .zero
    }
}

The result is this:

There is a gray border.

I have tried this:

1. setting view's, pdfWebView and pdfWebView.scrollView background with .white or .clear

2. webView.isOpaque = false ( this is the single one that removes the bottom part of the gray - but not the border)

3. I have used an extension to set the .clear color to all child views

   extension UIView {
       func clearBackgrounds() {
           self.backgroundColor = UIColor.clear
           for subview in self.subviews {
               subview.clearBackgrounds()
           }
       }
   } 
   

Nothing works to remove the border. I can not edit the pdf, because this one is downloaded from ws and used in multiple apps.