That depends on where it came from and what you want to do with it. If it's a .seq file from NI then it's a TestStand sequence file. To run it, you need TestStand. It is a text file and in theory you can use LabVIEW to open it and make changes just like any other text file but that's really for advanced TestStand users. The sequence editor in TestStand is the preferred way to make changes to a .seq file. NI's web page for TestStand is here with a link to an evaulation download.
