The thread seems old but for those who still haven't found any satisfactory solution should definitely try this Outlook PST to PDF wizard. This tool works perfectly and keeps the folder hierarchy intact. It also keeps the attachments embedded in their original format and provide multiple file naming options to save the converted PDF files.
There are many vendors in the market which provide such converter tools for PST to PDF conversion. Google it and you'll get plenty of options. Or if you don't wanna use any such paid software, you should use the virtual printer, called PDF Printer. Also, there's a built-in printer in Win 10, called Microsoft Print to PDF. If you're using the Adobe Acrobat Pro tool, you can use its built-in feature to save Outlook email as PDF file.