This depends on what CAD package you're using. In Inventor, you won't need to download CAD files. Everything you might need will be found in the
"Tube and Pipe" feature on the design tab of the ribbon. For Solidworks or Creo, etc. I can't answer the question.
If you need any help with anything Inventor related, feel free to contact me at
msimon@msedesign.net!