Hi Alejandro
It looks like you are using PI version 7.40, however the link that you are referring to is very old - probably XI3.0 so I don't think the parameters are valid anymore.
Anyway, AFAIK, sending multiple files only work with transport protocol NFS, and not with FTP. And this is achieved via checking the "Additional Files" box which is available with NFS only. Check the below SAP Help link for details.
Specifying Additional Files in the Sender File Adapter - Advanced Adapter Engine - SAP Library
For examples, you can refer to the following articles.
Sending Additional Files from SAP Netweaver PI to Third party FTP location
Sender File Adapter Frequently Asked Questions - Process Integration - SCN Wiki (check question 4)
If you switch to NFS, you can try adding an arbitrary name like PDFFile to the File list. Then add the following two parameters:-
PDFFile.namePart = ".xml"=".pdf"
PDFFile.optional = NO
Rgds
Eng Swee