For downloadable files i have set the path using following command :

this.Editor1.Setting["security:FilesGalleryPath"]= sPdfPath; 

The issue is :

that if we go to the properties window,
click style builder tab , 
then click background button in order to set the background image,
then click URL.. button and the browse window will open,

the folder path of that browse window is sPdfPath,
so how can we set the path for background images differently.