When you say you want those in the Save Box, do you want the static text of "PTLN, PTFN' or do you want the values entered into the userform text boxes?
If you want to pre-populate the default filename when you press F12, you should write that value to the document's Title property. eg
ActiveDocument.BuiltInDocumentProperties(wdPropert yTitle) = "This is a default filename"
In terms of errors on the second code, check your bookmarks actually exist. When your CommandButton1 code runs, it finds the bookmarks and writes text there but there is an insidious bug that removes the bookmark as part of that writing. So you need to reinstate the bookmark after setting the text value if you are going to need the bookmark in the document afterwards.
Code:
Dim PTFN As Range
Set PTFN = ActiveDocument.Bookmarks("PTFN").Range
PTFN.Text = Me.TextBox1.Value
ActiveDocument.Bookmarks.Add Name:="PTFN", Range:=PTFN
Refer to this link for some additional bookmark info
Working with Bookmarks in VBA.
I note also that your SaveForm code is not a replacement for the action of pressing F12 unless you have set that as a shortcut key.