Importing PDF - White Background vs Transparent

Hello,

I am an interior designer, and one service we offer clients is photoshopping exterior finishes onto 2D elevation drawings of their home's exterior, to show different colour/material options. 

Previously, I would import the PDF from the draftsperson and it would open with a completely transparent background, and only the black lines. Perfect.

All of a sudden now, it is importing with a white background, and in order for me to have the lines on their own layer with a transparent background to add in new images of colours/materials, I have to go through and delete every single white pixel.

I have very basic photoshop skills. Is there an easier way to do this?? 

I have tried asking the draftsperson to export the PDF a different way. They have even sent over PNG's of the elevations which still open in photoshop with a white background.

I tried adjusting the tolerances with the magic wand tool but it still doesn't get everything and I have to go back through to delete individual pixels.

Any help is appreciated!