TOPIC:

how to combine 2 or more pdf files in to single file ?

You can find example on how to merge 2 PDFs in the following KB article:

www.radaeepdf.com/support/knowledge-base?view=kb&kbartid=67

Thanks for the link you provided, is there a way to export or save the resultant PDF doc to stream ??

Thanks.

No, A modification that manipulates the PDF (add page, remove page, move page...) has deep impact on its structure and internal references; to reflect these changes the document must be saved, closed and then reopened..
So it cannot be exported to a stream.

Thanks for the information, for instance say i shall select 3 files using file picker & combine them & i want to save the combined file as storage file , how can i do this ?? could you please tell me.

Thanks.

This is a custom development, that you should handle using Windows SDK APIs..(selecting from file picker and create new storage file)

Regarding our SDK, you can use the example mentioned above along with the below method to save into storage file..You can also take a look into BrowsFileButton_Click in MainPage.xaml.cs