如何在iOS中使用PDFKit以编程方式从pdf文件中提取粗体文本？

guard let pdfURL = Bundle.main.url(forResource: "example", withExtension: "pdf") else {
    return
}

guard let pdfDocument = PDFDocument(url: pdfURL) else {
    return
}

for pageIndex in 0..<pdfDocument.pageCount {
    guard let page = pdfDocument.page(at: pageIndex) else {
        continue
    }
    
    // 在此处理每个页面的文本提取
}

let pageText = page.string

let attributedString = NSAttributedString(string: pageText)
let boldFontAttribute = [NSAttributedString.Key.font: UIFont.boldSystemFont(ofSize: 12)]

attributedString.enumerateAttributes(in: NSRange(location: 0, length: attributedString.length), options: []) { (attributes, range, _) in
    if let font = attributes[NSAttributedString.Key.font] as? UIFont, font.isBold {
        let boldText = (pageText as NSString).substring(with: range)
        print("粗体文本：\(boldText)")
    }
}