You can do this simply by right-clicking on the task and adding a "reference" to a new artifact - an attached file, form or hyperlink. (To learn more about the different types of artifacts supported in xProcess see Creating Artifacts in the Help system). Once you've done this, every time you make an instance of this pattern a clone of your artifact template will be created for use with that instance. Another nice feature is that you can substitute text in the file when you instantiate it, using the values that the user enters into the parameters of the pattern.
Actually parameters of patterns are discussed in the next article in this series, so see Using parameters in task patterns for more details.