Many times when you remove wallpaper, a layer of the drywall paper will come off also. This will expose an area of brown paper.
This can be skimmed over with drywall compound BUT the area needs to be treated properly.
If you skim directly over the brown area the moisture from the compound will cause the brown paper to curdle and create bubbles.
What you need to do is prime the area first. Go over the area using very little paint. Just enough to seal the area. When this coat is dry, you can apply another coat of primer.
When the primer is dry, the area can be skimmed, sanded and painted.
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