Stuck to save to PDF after binding the xml file

I have one program to convert the xml file into PDF using .save function after binding the xml. If the xml has no image in it, it was successfuly converted to a PDF from xml. If we put one image file in the xml file, like the following:

<Image File="/temp/logo.png" Type="png"></Image>

the following save API got stuck:

pdf1.save(new FileOutputStream(form1_pdf));

We need the help to check what is issue.