When I open a file with extension .plt, emacs behaves in a strange way. For example, I cannot type a space. I believe it has to do with something called the "PLT Package" because that name is displayed at the bottom of my window. However, no such package is listed in my .emacs file or in the list of packages accessible through emacs' menus.
I would simply like to remove/disable this package.
PS: In response to the suggestions so far, here is a screenshot that seems to indicate that "PLT Package" is related to a major mode.