VBA code affecting header unintentionally

So, I figured out how to add a defined text string to the end of the values in my cells, but now I have run into another issue.

I took a piece of code that I found from someone else with another question and I modified it (as best I could with my limited experience) to fit what I needed.

Long story short:

I am copying info from one excel workbook to a new workbook, each column has been changed so that they are in different orders. In column "E" in my new workbook I am adding the file extension ".pdf" to the end of the values that were copied over. The code I have thus far looks like :

Dim Myrange As Range, Mystr As String
    Application.ScreenUpdating = False
     
    Mystr = ".pdf"
     
     'If there are no constants then an error will be raised.
    On Error Resume Next
    Set Myrange = Intersect(ActiveSheet.Range("E:E"), ActiveSheet.Cells.SpecialCells(xlConstants))
    On Error GoTo 0
     
     'If there are no constants in Column A then exit
    If Myrange Is Nothing Then Exit Sub
     
    With Myrange
        .Offset(0, 1).Columns.Insert
        .Offset(0, 1).FormulaR1C1 = "=Concatenate(RC[-1], """ & Mystr & """)"
        .Columns(1).EntireColumn.Formula = .Columns(1).Offset(0, 1).EntireColumn.Value
        .Columns(1).Offset(0, 1).EntireColumn.Delete
    End With
     
    Application.ScreenUpdating = True

but the issue I have is that it is modifying my header "E1" to say "Document File Name.pdf" instead of leaving it as "Document File Name". I thought I would just get around my limited experience by having the macro alter the entire column, then tell it to change the value in E1 with

[E1].Value = "Document File Name"

right after the addition of the ".pdf" takes place. For some reason my coding runs through fine, no errors occur but I still end up with ".pdf" at the end of my header title, how can I get rid of this?


Sorry for all the questions but my work through me on this and I have no clue as to how to do it, neither do they but they want me to figure it out lol.