Opening a PDF File

Every time I try to open a saved PDF file in Excel, I get the following message:  "The file format and extension of 'chair quote.pdf' don't match.  The file could be corrupted or unsafe.  Unless you trust its source, don't open it.  Do you want to open it anyway?".  This really strange as I've saved a PDF file on 11/4 although it was a Word document.  I have never had this problem before in my some 30 years of using Excel.