No, topcoat is not same as primer, they have opposite roles in painting system, though both are coatings. Primer is first coat applied to bare, untreated surface to seal, bond, and create base for following coats, it has high adhesion, sealing properties, blocks stains and tannins, but is flat, porous, not washable, not UV resistant, and not durable as final finish. Topcoat is final finishing coat applied after primer and undercoat, it provides true color, sheen such as flat, satin, semi-gloss, is washable, durable, UV resistant, and provides protection and appearance. For example, in house painting, primer seals drywall, topcoat provides color and washability. In automotive, primer is under color, topcoat is color plus clear. Primer cannot serve as durable topcoat, topcoat cannot seal bare wood like primer. Some products are labeled primer and topcoat in one or self-priming paint, which combines both properties, but traditional primer and topcoat are different. So primer is base layer for adhesion and sealing, topcoat is final layer for color and protection, they are not same and should not be interchanged, though combined products exist.
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