Attach files using the GAPI

Question:
How can files be attached to a stored document using GAPI?

Answer:
An easy example, how to attach files to a stored document, using the GAPI, could look like the following:

IInsertCommand dokInsert = document.Commands.newInsert();
dokInsert.AddDocumentToInsert(gapiClient.GetDocument(new string[] { "C:\\Temp\\GAPI\\DOCU0001.001" }));
dokInsert.Execute();