Can't see things outside of the artboard on Illustrator

[Nicholas32139075y31a]

So last night I got a file template that was a pdf for a project. I proceeded to do work within that PDF in Illustrator and ended the day by saving it into the sent file (So it was saved as a PDF). When trying to open it today, the file previews as all the work I did on the home page, but when opened, it only shows everything on the artboard, not all the work I did on the side of the artboard. Can anyone please help so I can see all the stuff outside the artboard?

[Doug A Roberts]

If the file was saved without Illustrator editing on, those additions are lost to Illustrator.

[Nicholas32139075y31a]

So even though it was saved on Illustrator as a PDF file it is completely lost? Then why does it preview correctly on the illustrator home page correctly?