Yes it is possible to add documents to the document library from code, use the CopyIntoItems method of Copy service
CopySoapClient client=new CopySoapClient(); client.CopyIntoItemsCompleted += new EventHandler<copyservice.copyintoitemscompletedeventargs> (client_CopyIntoItemsCompleted);
client.CopyIntoItemsAsync(sourceUrl, destination, fieldInfo, byteArr);
where sourceUrl is the name of the file to be uploaded
destination is the includes "SharePointSite"+"DocumentLibrary"+"FileName".
fieldInfo is the Field information.
ByteArr is the File as stream.