Do I need to remove the door panels to install these?

No. These covers mount over the existing handles from the outside — panel removal isn't necessary. Locate the factory fastening points on your handle and secure the covers in place.

Will I need adhesive, screws, or both to attach them?

Mounting hardware and method aren't specified in the product data. Test-fit the covers first, then decide whether to use mechanical fasteners or adhesive based on how they seat. Your Passat's original handle design will guide the best approach.

Can I paint these to match a custom color, or do they need prep?

ABS plastic takes paint, but surface prep is essential — light scuff and degrease before any primer or color coat. Since these ship with a textured finish, the grit itself may help adhesion. Sand if the texture feels too aggressive for your paint method.