Hi Tal,
There is a certain prerequisite that user should be assigned in 105 infotype subtype 0001 to be able to insert elements using WDA you mention.
You may use ORGANIZER transaction to create the files. Please also consider that from what I know official SAP position is that DPF is to be used only to store P&F results. So such usage appears to be not standard.
Regarding authorization you may achive something depending on how you build a structure of your DPF, please see authorzation possibilities here.
https://help.sap.com/erp_hcm_ias_2012_01/helpdata/en/06/8c71c8b2004fe29d7abccfeb5f6aa9/content.htm
Good luck.
Vladimir