Private Sub Command1_Click()
Dim F
F = FreeFile
Dim mytext
 Open "C:\1\1.txt" For Input As #F
Do Until EOF(F)
 DoEvents
Line Input #F, mytext
Dim x As Long
For x = 1 To Len(mytext) - Len(Text1.Text) + 1
If Mid(mytext, x, Len(Text1.Text)) = Text1.Text Then MsgBox Text1.Text
Next x
Loop
Close #F
End Sub

Imports System
Imports System.IO
Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim PathBl As String
        PathBl = "C:\1\1.txt"
        Dim fi As New System.IO.StreamReader(PathBl, System.Text.Encoding.GetEncoding(1251))
        Dim mytext As String
        Dim x As Long


        mytext = fi.ReadLine()
        Do While Not mytext Is Nothing
            For x = 1 To Len(mytext) - Len(TextBox1.Text) + 1
                If Mid(mytext, x, Len(TextBox1.Text)) = TextBox1.Text Then MsgBox(TextBox1.Text)
            Next x
            mytext = fi.ReadLine()
        Loop
        fi.Close()
    End Sub
End Class

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim PathBl As String
        PathBl = "C:\1\1.txt"
        Dim fi As New System.IO.StreamReader(PathBl, System.Text.Encoding.GetEncoding(1251))
        Dim mytext As String
        Dim x As Long
        Dim y As Long

        mytext = fi.ReadLine()
        Do While Not mytext Is Nothing
            For x = 1 To Len(mytext) - Len(TextBox1.Text) + 1
                If Mid(mytext, x, Len(TextBox1.Text)) = TextBox1.Text Then
                    For y = x + Len(TextBox1.Text) - 1 To Len(mytext)
                        If Mid(mytext, y, 1) = " " Then
                            MsgBox(Mid(mytext, x, y - x))
                            Exit For
                        ElseIf y = Len(mytext) Then
                            MsgBox(Mid(mytext, x, y - x + 1))
                        End If
                    Next y
                End If
            Next x
            mytext = fi.ReadLine()
        Loop
        fi.Close()
    End Sub

Public activeTextBox As TextBox

    Private Sub TextBox_Enter(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.Enter, TextBox2.Enter, TextBox3.Enter
        activeTextBox = CType(sender, TextBox)
    End Sub

    Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click
        'activeTextBox.Text = activeTextBox.Text & "This is text 1"
        activeTextBox.Text = activeTextBox.Text & "й"
    End Sub