Corrupt document upload?

We have created a marketing request form. We just had a submission come with an attempted document attachment. When we try to open the document, we get a weird error message (see attached).

Could you please help me understand what happened here?

Thanks,
Ginger

I just did a test submission, and it went through successfully. Seems like that PDF file was corrupted, that's why it shows the error even though it was successfully uploaded.