You should use the Word.Section.Headers property, in the example below I put the image aligned to the right in the page header
foreach (Word.Section section in newDocument.Sections) { string picturePath = @"D:\Desktop\test.png"; section.Headers[WdHeaderFooterIndex.wdHeaderFooterPrimary].Range.InlineShapes.AddPicture(picturePath); section.Headers[WdHeaderFooterIndex.wdHeaderFooterPrimary].Range.ParagraphFormat.Alignment = WdParagraphAlignment.wdAlignParagraphRight; }
To add some use of text:
foreach (Word.Section section in newDocument.Sections) section.Headers[WdHeaderFooterIndex.wdHeaderFooterPrimary].Range.Text = "TEST";
Hope this helps to research further.
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