Visual Studio UI – how do I make it clear that a button should NOT normally be clicked?

I've written an app for my company that watermarks images we've created and compiles them into a pdf to send to the client. However, rarely, clients will request unwatermarked images: so there needs to be a secondary button to just compile the images without watermarking them.

I want it to look clear that "Watermark All" is the standard and that "PDF Only" is only for rare cases. I've tried making the PDF only button darker, but then it just looks locked/unclickable.

How do I encourage users to click the watermark button unless they've been told otherwise?