使用mPDF从多个PDF文件生成单个PDF时，锚标记不起作用

Question

I have three PDF files. I want to integrate three PDF files into a single PDF file. I have used mPDF library to generate single PDF file from multiple PDF files.

$mpdf = new mPDF('en', 'A4-L');
$mpdf->SetSourceFile("1.pdf");
$tplId = $mpdf->ImportPage(1);
$mpdf->UseTemplate($tplId);
$mpdf->SetSourceFile("2.pdf");
$tplId = $mpdf->ImportPage(1);
$mpdf->UseTemplate($tplId);
$mpdf->SetSourceFile("3.pdf");
$tplId = $mpdf->ImportPage(1);
$mpdf->UseTemplate($tplId);
$mpdf->Output("output.pdf", "D");

When generating a single PDF file, I can not see anchor URL into the text in PDF file.

Sample PDF File Here