Thanks for taking the time to contact us about this.
It’s rare that we receive a feedback like yours, even though we have a dedicated team working relentlessly to implement the feedback back we receive.
I do understand how convenient it would be for all our customers if this feature to open PDF files on your Kindle for Windows app is implemented.
To make sure that your comments are heard by the right people in the organization, I've forwarded your message to our Kindle development team so they can look into the possibility of implementing this option soon.
As with all of our products, we continue to make Kindle and Kindle apps better for customers with regular software updates. Customer feedback like yours is essential in helping us determine what additional features our visitors and customers want most.
As soon as this feature becomes available, we will definitely let you know about this through our website.