"Combining documents"

Hello there.  I'm new to Rapid-i.  I've managed to mine a really good data set from the web using the web crawl function, and now have over 500 txt files of source code of target pages.  I've tried to use the combine documents function to combine these into 1 file (so I can then parse it all in one go), but am having difficulty.  I don't know how to specify the multiple target txt files as inputs.  There is no real help for this function and it is not detailed in the guidebook.  Very grateful for any assistance!!!