Hi Cerbero,
To process multiple files into single message, you need to use ccBPM.
See below example for 2 files:
http://****************/Tutorials/XI/BPM/Fork1.htm
For the requirement of not overwriting, see below:
Select the File Construction Mode.
○ Create
The file is created. The document received last is saved in each case.
If you want the created file to be overwritten, set the Overwrite Existing Fileindicator. If you do not set the indicator, processing is stopped until the created file is processed.
Regards,
Nabendu.