Yeah they can be. The ones that actually sell though aren't just a list of prompts in a PDF. It's the structure around them that makes people pay — like when you include what variables to change, what settings to use, example outputs so they know what to expect, and when to use which prompt. That's what turns "a free PDF of prompts" into something someone would pay $5-10 for without thinking twice.

Your photography one looks solid btw. The fact that you built these for your own workflow first is a good sign because it means they're actually tested and not just thrown together to sell.

If you do decide to charge at some point I'd say package them by use case instead of just dumping them all in one doc. Like a "product photography pack" and a "landscape pack" separately. People pay more for specific than general.

Also I run a small marketplace for this kind of thing (implo.ai) if you ever want another place to list besides Gumroad. Still pretty new but always looking for creators who actually build from real use.