Issues with Copy/Paste producing blank text

I have PDFs that are generated using wkhtmltopdf that do not allow me to copy/paste the text.  When I try to paste the text, I get blank spaces.  I am able to copy/paste properly from acrobat and adobe reader.  I have a sample document that was generated and is not working via the link below.  I have tried both PDF Architect 1 and 2 and both have the same issue.

Sample PDF: