For office developers, you might want to check is there any existing active document is opened before you open a document template. What you can do is, check is there any open by using ( Globals .ThisAddIn.Documents.Count > 0). Then close the activeDocument...

Missing this reference " Office = Microsoft.Office.Core "? Here is how you can add the particular reference: Step 1: Right-click your project Step 2: Select " Add reference.. " Step 3: Click on the " COM " tab Step 4: Scroll down to select " Microsoft...