Well I painted the roundels on my RCAF mustangs. They look OK and since my opponent doesn't see my models during covid lock-down they will pass. I will be buying decals for any future repaints.
If you can edit Adobe Acrobat, maybe you want a pdf with vector images. Modify numbers, letters, roundels, drawings..... scale at high resolution to virtually unlimited sizes and use water slide decal paper. A png example of Hawker Hurricane markings: