You do not talk about why you want to do this conversion. Suppose you have old documentation saved as old fashioned physical sequential files on the mainframe and you want to convert them to pdf to publish in your library in the intranet.
There are many ways to do it:
– ftp them, open it with OpenOffice, save as PDF
– ftp the file, by a tool from Adobe (Framemaker, Destiller), open the file with the tool and save it as PDF
– write your own program (for example, in Java using iText) and convert it.
There are products available to do this – convert a mainframe file (probably a report) to PDF format. for example XMITIP.