[Adi Mona]

For each clip you should have a provided matte
lets just say you’ve got 0001_DElement.mov and 0001_DElement_Matte.mov

Just import both clips into AE,
drop them both into the timeline (With matte on top) and hide the Matte layer
from the effects menu go to “channels” and add “Set Matte” to the original clip
In the Effects Control window (for the original clip) set the “Take Matte From Layer” to your matte clip 0001_DElement_Matte.mov
and Finlay Set “Use For Matte” to “Luminance”.

I hope this can help.