https://stackoverflow.com/a/58308215/1271826

RemoveAnnotations.swift

func removeAllAnnotations() {
    guard let document = document else { return }
    
    for i in 0..<document.pageCount {
        if let page = document.page(at: i) {
            while page.annotations.count > 0 {
                page.removeAnnotation(page.annotations.last!)
            }
        }
    }
}

func removeAllAnnotations2() {
    guard let document = document else { return }
    
    for i in 0..<document.pageCount {
        if let page = document.page(at: i) {
            for j in (0..<page.annotations.count).reversed() {
                page.removeAnnotation(page.annotations[j])
            }
        }
    }
}