Hello Trung,
I created and uploaded a sample application to support at Gizmox, I'm not sure what will happen from there. I'm not quite sure what you are refering to about auto-fill of the fields, but for example if you create a table of 2 rows and 3 columns, you can just keep adding to it and it will expand for every row. If you mean you can use it as an input form, I'm not sure that is possible without a commercial version of Acrobat.
In any case, I hope the example will help get you started, you can use the iTextSharp libraries to also create RTF, HTML and XML reports also, and the gateway uses urlmon.dll to identify the MIME type so the gateway works with other types than PDF.
Good luck and best regards, Kenn