issue with ppt not opening my file and some other saved files.

hi I would like apple fix my issue since now all shops are closed so this is the only to contact with apple or IStyle... so In my MacBook air I saved a file in powerpoint as pdf yesterday when I tried opening it to make changes and add some stuff it doesn't open I can just open it from the desktop but I want to open it from ppt like I usually do so I can make changes there but it says :"powerpoint can't open this type of file (CAREER PROJECT copy.pdf)."

I tried saving it to different place to try if it opens in ppt but its the same also one time it said its from unidentified developer so I have to change in settings to "anywhere" but Idk how to do it since this option is not there....

so if you pls fix my issue it will be great even-though its not opening I wanted to do a new file because my project is due tomorrow but when I type the box in ppt disappear.