So if you have Nuance software does Image retriever notify you that the scan is completed?
In Windows 10, what is the default app for opening PDF? You can check by using Default Apps in Windows 10, if you just blindly updated to Windows 10 and chose to Use Express Settingsthen all your defaults would have been replaced with the MS supported way. And in this case, pdf would be opening in Microsoft Edge which won't work.
Here is the lowest versions Nuance supports for Windows 10 and pdf.
Have you used Nuance's forum? Since your issue is their software they would likely be better equipped to handle the issue. I know they don't officially support Windows 8.1 or higher last I checked, but you used to be able to just install their stuff in Compatability Mode = Windows 7