To display an Adobe Acrobat file you must have a separate program installed on your computer?

It depends on what operating system you are running.

If you are on Windows, you can download (for free) Adobe Acrobat Reader.

If you are running Mac OS X, the pre-installed Preview program can display Adobe PDF files. You can also download Adobe Acrobat in case Preview does not work for some reason. Previous versions of the Mac OS require that you download Adobe Acrobat Reader.

Linux

If you run Linux, you either have Document Viewer, KPDF, or Evince, all of which can open Adobe PDF files.