This error may happen because the formatting that we use for our PDF viewer cannot read this PDF.
To fix this:
1. Open Bluebeam > File > Create
2. Select the file and then click Open and Save the file and then reload in Estimator.
Another method that can be used is to open the PDF in the PDF Viewer (Bluebeam or Acrobat) and export the PDF as a JPG image and try loading that in Estimator. If that works, then you can use steps 1-2 above to recreate the PDF.