Individual certificates or full inventory generating in HTML format

When clicking on generate individual certificates or generate full inventory they printout in HTML format. It is possible that the utility that generates the PDF report has become corrupt and or needs to be installed. This can be installed with an internet connection. Once an internet connection is established open up a terminal window and type, 

sudo apt-get install wkhtmltopdf

and hit return. The installation will take seconds. Once that is done try to rerun the reports.