Quote:I improved my question
Quote:could not be resolved because it was built against the ".NETFramework,Version=v4.6.1" framework. This is a higher version than the currently targeted framework ".NETFramework,Version=v4.5.2"
This tells you what you need to know: the DYMO libraries use a higher version of the .NET Framework than your app - which means you can't call them as you can't "mix frameworks" in the same process. You can use lower versions provided the process starts at the higher one, but not the other way around. It's a bit like plugging a USB adapter into the mains: you can plug anything that expects USB voltages into it, like your phone, a 3D printer, a tablet. But you can't plug your TV into it as its far too low a voltage for it to run!
You need to change the framework version of your app - go to the Solution Explorer pane, open your project branch, and double click the "Properties" twig. The .NET version is at the top right of the page it displays. Almost certainly, you will have to close and re-open the project to commit the change.