In order to replace a text in any section of the header or the footer of a word document, you can use this snippet
doc = Document Object
foreach (Section sec in doc.Sections)
{
foreach (HeaderFooter fot in sec.Footers)
{
fot.Range.Find.Execute(FindText: loc.Key, ReplaceWith: loc.Value,
Replace: WdReplace.wdReplaceAll);
}
}
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