Sorry I didn't read the post clear enough the first time, and didn't explain my code enough so it got deleted. This uses the contentclick event.
Dim Filetext As String = "" 'At start of the class to make it available to the whole class
Private Sub DataGridView1_CellContentClick(sender As System.Object, e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellContentClick
Dim FilePathColumn As Integer = 0 'File path is in Column 0
Dim ButtonColumn As Integer = 1 'Column buttons are in
Dim RowClicked As Integer = e.RowIndex 'This gets the row that you clicked the button in
If e.ColumnIndex = ButtonColumn Then 'Make sure you clicked a button
Dim FILE_PATH As String = DataGridView1.Rows(RowClicked).Cells(FilePathColumn).ToString 'Get the path to the file
If System.IO.File.Exists(FILE_PATH) Then 'Make sure file exists
Filetext = System.IO.File.ReadAllText(FILE_PATH) 'Save file to a variable
'OR
Process.Start(FILE_PATH) 'To open it
End If
End If
End Sub
You can get rid of most of those lines but I wrote it like that to explain how it worked