The word doppelganger is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 25
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (47 words)
aerogel, angered, dangler, deplane, deplore, derange, doppler, eggdrop, engaged, engorge, enlarge, enraged, gargled, general, gleaned, gleaner, gnarled, goldpan, grapple, grenade, groaned, lagered, learned, leopard, operand, paneled, papered, paroled, pearled, peopled, peregal, pergola, pleader, pledger, predeal, preload, prepend, preplan, pronged, propane, propene, redpole, relodge, repaged, repanel, replane, replead