"...not a valid photoshop document" fix?

So I have this PDF file that I made and I saved. I was able to open it yesterday but now today it won't. My computer crashed while I was working on it. I don't think that is it because that happened TWICE and the file was there to open. But now, even if its a PDF file, it won't work, I keep getting an error saying "...not a valid photoshop document" How do I fix this?!

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