Section.HasHeader(HeaderFooterType) Method

Document document = server.Document;
Section firstSection = document.Sections[0];

// Check whether the document already has a header (the same header for all pages).
if (firstSection.HasHeader(HeaderFooterType.Primary))
{
    //If not, create an empty header
    SubDocument headerDocument = firstSection.BeginUpdateHeader();
    headerDocument.Paragraphs.Append();
    firstSection.EndUpdateHeader(headerDocument);
}

Dim document As Document = server.Document
Dim firstSection As Section = document.Sections(0)

' Check whether the document already has a header (the same header for all pages).
If firstSection.HasHeader(HeaderFooterType.Primary) Then

    ' If not, create an empty header
    Dim headerDocument As SubDocument = firstSection.BeginUpdateHeader()
    headerDocument.Paragraphs.Append()
    firstSection.EndUpdateHeader(headerDocument)
End If