Black boxes in pdf underlay?

[kevinVKVXX]

When opening up a pdf, what's odd is sometimes black boxes occur on areas of the drawing (see bottom left of image). Any ideas as to what is causing this or how to fix?

[Mike_Arcari]

I get this occasionally on estimator

try turning off the particular layer that contains the black boxes

if its linked to something you need then try changing the colour of the layer to white or black