Acrobat has the loadfile() method, which is loading and refreshing without closing the window.
In the htmlviewer there is the navigate() method, which does the same.
i found that harbour Code and i have test it with Xbase++ and Ot4XB and it work.
but that piece of Code does not present all what can be done when using SumatraPDF
you can start SumatraPDF as Stand-alone. in upper-left you find a Menu.
you can use multi Instance or "ReuseInstance"*** but that was not include in my harbour Code
*** https://www.sumatrapdfreader.org/settings.html
so i have to ask in harbour Forum how to use "ReuseInstance"