can't save .odt!!!

Dear All!
When I try to save an .odt documet on the desktop of my pc, I click “.odt” when SAVING, but when I try to open it, it apperas in pdf format which I can’t open.

Does it now look strange?
What might be a cause and can I fix it alone, without calling the admnistrator?
Thanks!

Can you save documents in other places? Are you sure you are not trying to open a PDF version of the file you are trying to save? What version of LibreOffice are you using and what operating system?