Is there a way to change the default save/export format in Preview? I always choose PDF when exporting and usually choose JPG when saving. Being able to change the default format from PNG to either of these would save me a few clicks every time I use Preview. Is there a way? Preview preferences has no save/export format option, and I was unable to find anything on Google.

For bonus points, is there a way to have the default extension for images saved in JPG format with Preview be .jpg instead of .jpeg? It's a pain to change them manually every time, and leaving them means having to remember which files are .jpg (those not from Preview) and which ones are .jpeg (those from Preview) when making websites.

Thanks in advance.
Normally, Preview saves a document in whatever format the graphic image was imported. The only circumstance when a document in Preview has no pre-existing file format is when data is pasted from the clipboard.

There does not seem to be a known preference key for changing the default file format in Preview under this circumstance.

For me (on Mojave 10.14.5), Preview exports JPEG files as .jpg. 

Both .jpg and .jpeg are valid file extensions, and there should be no difficulty in having both in a website. If you can't stand the chaos, you can easily batch process files in the Terminal with a script like this:

for file in *.jpeg; do mv "$file" "${file%.jpeg}.jpg"; done


which will work on all files in the current working directory.