$search_res = $search-> {Text} = "\x{0021}";
$replace-> {Text} =  "\x{0022}";
$exec_res = $search-> Execute({Replace => wdReplaceAll});
$selection->InsertSymbol( { Font=> "Wingdings", CharacterNumber => -40
+63, Unicode => 1 });
[download]

I'm not an expert on the Word Object Model, but I did find Word Object Model Reference, which looks worth a read (if only as a cure for insomnia).

I cannot see a property of the Find Object which gives the position of a successful find... I do, however, note that you can set a Font property. You can also set the Font property of the Replacement Object. My guess is that you can use the Unicode "private use" character values used for Wingdings (ie 0xF000 + 0x21 ("\x{F021}") for Wingdings "pencil at 45 degrees") plus the font name for find or replace.

I note also that a Selection Object can have a Find property... which looks plausible ?

Thank you for everyone’s suggestions. I have looked at the various references and also ‘googled' for a solution.
Frustratingly I found places where the insertion point was mentioned and even questions about how to ‘set’ it
but no answers using either VBA or Perl code.
Therefore I used the recording macro facility with Word to locate a character hoping that this would give a clue about what to do. This gave the following

Selection.Find.ClearFormatting
With Selection.Find
.Text = "!"
.Replacement.Text = ""
.Forward = True
.Wrap = wdFindContinue
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
End With
Selection.Find.Execute
Selection.MoveRight Unit:=wdCharacter, Count:=1
Application.Run MacroName:="Normal.NewMacros.insertsymbol"
[download]

I was not really sure what to do but I did make an attempt and included it in another Perl test.
I ignored the last line and simply used what I knew should work to add a wingding character. The code is below

use strict;
use Win32::OLE;
use Win32::OLE::Const 'Microsoft Word';
# set $filepath to the full path to the direcotry where the file to be
+ changed, test.doc, is stored
my $filepath = 'C:\tmp';
my $oldfile = $filepath . '\wingding1.doc';
my $newfile = $filepath . '\wingding1-edit.doc';
my $word = Win32::OLE-> GetActiveObject('Word.Application')
    || Win32::OLE-> new('Word.Application','Quit');
my $doc = $word-> Documents->Open("$oldfile");
# is application visible 0=no  1=yes
$word-> {visible} = 0;
my $selection = $word->Selection; # select current position
# start of Word macro conversion
$selection->Find->ClearFormatting;
$selection->Find ( Text => "!",
    ReplacementText => "",
Forward => 1,
Wrap => wdFindContinue,
    Format => 0,
    MatchCase => 0,
    MatchWholeWord => 0,
    MatchWildcards => 0,
    MatchSoundsLike => 0,
    MatchAllWordForms => 0);
$selection->Find->Execute;
$selection->MoveRight ( Unit => wdCharacter, Count => 1);
$selection->InsertSymbol( { Font=> "Wingdings", CharacterNumber => -40
+63, Unicode => 1 });
# save word file
$word-> ActiveDocument->SaveAs($newfile);
# close word file
$doc-> Close();
$word-> Quit();
[download]

I used this with a document with a ! towards the end of the first line. Sadly this still put the inserted
wingding at the beginning of the document. I even tried with just Text => "!" in the ->Find
(partly because I was not at all sure that Replacement.Text should be converted as
ReplacementText) but this also did not work.
Has any Monk an idea how to make this work?

You need to set $selection to be where you want to insert your symbol. However you do that with Word. I suggest reading the Word documentation on how to set the selection to a specific position, or even better, how to set the selection to a string that was searched.