Urgent how DOCX(Xstring) is converted to PDF(Xstring)

can someone help how can I convert DOCX(Xstring)  to PDF(Xstring) as i want to attach it to VF03 transaction.I am getting DOCX(Xstring) i want it to convert to PDF(Xstring) and attach in the VF03 as PDF File. 

 

Thanks in advance!