Sub Demo()
Dim wdDoc As Document
Set wdDoc = Documents.Open(FileName:="C:\Users\rahul\Desktop\PLR\1.rtf, Format:=wdOpenFormatText, AddToRecentFiles:=False)
With wdDoc
  'process here
  .Close SaveChanges:=True
End With
End Sub

Sub EditRTFFile()
'Requires a reference to Microsoft VBScript Regular Expressions 5.5
Dim DataFile As String, TextLine As String, Data As String, regEx
DataFile = "C:\Users\rahul\Desktop\PLR\1.rtf"
Set regEx = CreateObject("vbScript.RegExp")
Data = ""
Open DataFile For Input As #1
Do Until EOF(1)
  Line Input #1, TextLine
  On Error Resume Next
  With regEx_
    .Global = True
    .MultiLine = True
    .IgnoreCase = True
    .Pattern = "\{\\\w{4}\\\w{4}\\\w{11}"
    TextLine = regEx_.Replace(TextLine, "mmrk$&")
  End With
  Data = Data & TextLine & vbCrLf
Loop
Close #1
Open DataFile For Output As #1
Print #1, Data
Close #1
Set regEx = Nothing
End Sub