Welcome to the forum.
Here is a thread that address your question on backsaving to previous versions.
The bottom line is you can't. Solidworks is not backwards compatible. The only
way is if you export your models out as igs, step or parasolid files then import
those into the lower version.
As far as your other question, the .stl files are already an option in your models under
the save as file type menu.
and the pdf is under the file>save as in the drawing mode.
you can also print to pdf as well if you have the print drivers setup.
Not with the .stl and pdf there may be an issue that they are not there
as options of you have the student edition.
Thanks for the reply, how can I get the file extensions for all the file types? Is there a package or somthing?
I'm guessing you have the educational version. It is very limited in what types of files you can export.
Like I said in my first posting and Josh comfirmed, if you are not seeing these it is because
you have the student or educational version.