the point is to create a new blank layer, then select this layer, apply the filter and therefore open the file.
the other way; when you got a layer previously filled with text, brush drawing or anything; is to make a selection of this layer.
then create a new layer and paste, finally you can apply blend+ filter to this layer. remember to uncheck the view of the previous layer
as i said i wish there was transparency directly in. but the main thing is there's no mask in PDN