Photoshop 'Save As' defaults as PDF

Hello,

I had recently opened a PDF file in Photoshop and made no changes to the file and ended up closing the file. Now going forward whenever I open a file, whether I make a change or no change to the file it defaults to 'Save As' with the filetype .PDF. For example, if I open a Jpeg and save it upon opening without any action it defaults to a 'Save As' dialogue box with the .PDF filetype extension. 

How can I reset this to save filetypes to their respective extensions?

Thank you,