You can easily import MBOX files to PDF format by using ZOOK MBOX to PDF Converter tool. It is designated tool to convert or save MBOX files to PDF format with complete mailbox data and attachments. This tool kept intact all email formatting and hierarchy throughout the conversion process. It is capable to convert MBOX files of all major email clients like Mozilla Thunderbird, Entourage, Netscape, Opera Mail, Yahoo Mail and man others. It is completely professional tool to convert, save or print MBOX mails to PDF. 

For more info- https://www.zooksoftware.com/mbox-to-pdf/