新人求助，请各位来帮帮忙！

Private Sub Command1_Click()
    Dim i As Integer, num As Integer
    Dim filePath As String
    Dim strTemp As String, str1 As String

    i = FreeFile
    filePath = "d:\1.txt"
    '将内容读取到strTemp="aaabbbddd",这里只针对你所说的情况,如果其它复杂一点的,你就要好好研究下读写文件了
    Open filePath For Input As #i
    Do While Not EOF(i)
        Input #i, strTemp
        str1 = str1 & strTemp
    Loop
    Close #i
    'str1转换
    str1 = Replace$(str1, "d", "c")
    i = FreeFile
    '保存到 txt 中
    Open filePath For Output As #i
    Print #i, str1
    Close #i
End Sub