Infopath Can't Get Selected Document Data

I'm a newbie in Sharepoint Development.

I tried to create a document library using InfoPath. I wanted to get "Created By" column data and use it on a field in Infopath. I followed the steps from this link I already created a new data connection and binding the field to DisplayName under Created By. But it always display same username. So, I checked it and found that the data connection only retrieve the first Document data in the library.

May someone tell me, how to get the selected document data from SP to Infopath form?