Hi,
I am not sure why you want to do because you can save your noise data as a text file and import it directly to Multisim. The only reason why you would want to bring a tdm file into Multisim is if your VI is setup to save tdm file and don't want to convert the data.
In Multisim use a Piece Linear Wise (PWL) source, it's located under the "Sources" group, "Signal voltage source" family. Place the source on the workspace, double-click and there should be an option to load a .txt file.
Tien P.
National Instruments