Use ADO and the Jet OLEDB provider, which can read the contents of excel files without actually opening Excel.

Example:

'*******************************

Public 

Sub ConvertXLSToTab(

ByVal xlsFileName 

As 

String, 

ByVal tabTextOutputFile 

As 

String) 

        

Dim connectionString 

As 

String = 

"

Provider=Microsoft.ACE.OLEDB.12.0;Data Source='

" & xlsFileName & 

"

';Extended Properties='Excel 12.0;HDR=YES';

"

        

Dim strSQL 

As 

String = 

"

SELECT * FROM [Sheet1$]

"

        

Dim excelConnection 

As OleDb.OleDbConnection = 

New OleDb.OleDbConnection(connectionString)

        excelConnection.Open()

        

Dim dbCommand 

As OleDbCommand = 

New OleDbCommand(strSQL, excelConnection)

        

Dim dataAdapter 

As OleDbDataAdapter = 

New OleDbDataAdapter(dbCommand)

        

Dim ds 

As 

New DataSet

        dataAdapter.Fill(ds, 

"

dTable

")

        

'

DataGridView1.DataSource = ds.Tables("dTable").DefaultView

        

Dim strLine 

As 

String

        

Dim objStreamWriter 

As StreamWriter

        objStreamWriter = File.CreateText(tabTextOutputFile)

        

For 

Each row 

As DataRow 

In ds.Tables(

"

dTable

").Rows

            

Dim column 

As DataColumn

            strLine = 

""

            

For 

Each column 

In ds.Tables(

"

dTable

").Columns

                

If (strLine <> 

"") 

Then strLine = strLine & vbTab

                strLine = strLine & row(column).ToString()

            

Next column

            objStreamWriter.WriteLine(strLine)

        

Next row

        excelConnection.Close()

        objStreamWriter.Close()

    

End Sub