TIFF Viewer Pro and TIFF Viewer Regular feature comparison:

FeaturesTIFF Viewer StandardTIFF Viewer Pro
  Purchase Standard Purchase Pro
View, Print TIFF, FAX documents    
Annotate TIFF, FAX documents    
View, Print PDF documents    
OCR TIFF, FAX documents    
OCR PDF documents    
Search TIFF, FAX documents    
Search PDF documents    
PDF Form Filling    
Fully Configurable    
Internet Explorer Browser Plug-In    
Chrome / Edge extension    
MSI Installer    
 Pricing Starts At $ 39.99 / Annually $ 79.00 / Annually

For upgrading TIFF Viewer Standard Edition to Pro Edition, please re-register the TIFF Viewer with a Pro serial number. No reinstallation is needed.