If you don't regularly open files with administrator privileges, there's no need to add the "Run as Administrator" option to the file. Instead, hold "Ctrl-Shift" while clicking a program from the ...

Press "Ctrl-O" in Adobe Illustrator to bring up the Open window. Alternatively, click "File" and "Open." Click the "Files of Type" drop-down menu and select "AutoCAD Drawings (*.DWG)." Navigate ...

Word will select both of the clicked files and all the files in-between. Nonadjacent files: To select non-contiguous files, hold down [Ctrl] while clicking each file you want to open.

In a Finder window, right-click (or Ctrl-click) the file whose default launch app you want to change. From the contextual menu, select Open With -> Other.