USE AdventureWorks;
GO

CREATE TABLE myTable(
	FileName nvarchar(60), 
	FileType nvarchar(60), 
	Document nvarchar(max));
GO

ALTER TRIGGER myTrig 
ON myTable
INSTEAD OF INSERT
AS
	DECLARE @filename nvarchar(60);
	DECLARE @filepath nvarchar(60);
	DECLARE @sqlstmt nvarchar(4000);
	DECLARE @document nvarchar(max)

	SELECT @filename = Filename FROM inserted ;
	SET @filepath = 'D:\' + @filename +'.txt';

	set @sqlstmt = 'SELECT @docout = BulkColumn FROM OPENROWSET(BULK ''' + @filepath + ''', SINGLE_CLOB) AS Document;'
	select @sqlstmt
	      
	exec sp_executesql @sqlstmt, N'@docout nvarchar(max) OUTPUT', @docout=@document output
	
	INSERT INTO myTable select i.filename, i.filetype, @document from inserted i

GO