To ensure special characters as, for instance, Æ, Ø and Å are included and properly shown in your merge document, and in general your uploaded CSV file, you must convert your CSV file into an UTF-8 format.  

On Windows: Open your CSV file in Notepad by right clicking on the CSV file and choose “Open in” and then “Notepad”. Now, save your CSV file again. The filename must end with .csv to ensure the CSV format.

“Save as file type” is a drop-down menu below the filename field and here choose “All types”. The last thing you have to do is to choose UTF-8 in the drop-down menu in the lower right corner of the Window.