Apply a style to a paragraph in a word processing document

Paragraph styles are referenced from paragraph properties with <w:pStyle/>. The style definition lives in word/styles.xml.

Applying a style requires both a paragraph reference and a style id. The style id is the stable value used in markup; the friendly style name can be different, such as Heading 1 for the style id Heading1.

Style reference markup

<w:pPr>
  <w:pStyle w:val="Heading1"/>
</w:pPr>

If the target paragraph has no <w:pPr/>, create paragraph properties before adding <w:pStyle/>. Paragraph properties are the place for paragraph-level formatting such as alignment, indentation, borders, line spacing, shading, text direction, and style references.

Rust workflow

Verify the style id exists, then update the first paragraph's paragraph properties:

#![allow(unused)]
fn main() {
pub fn apply_style_to_first_paragraph(
  path: &Path,
  style_id: &str,
) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
  let mut document = WordprocessingDocument::new_from_file_with_settings(path, lazy_settings())?;
  let main_part = document.main_document_part()?;
  let Some(styles_part) = main_part.style_definitions_part(&document) else {
    return Err("document has no styles part".into());
  };
  let styles_xml = styles_part.data_as_str(&document)?.unwrap_or_default();
  if !styles_xml.contains(&format!(r#"w:styleId="{style_id}""#)) {
    return Err(format!("style {style_id} not found").into());
  }

  let document_xml = main_part.data_as_str(&document)?.unwrap_or_default();
  let updated_xml = set_first_paragraph_style(document_xml, style_id)?;
  main_part.set_data(&mut document, updated_xml.into_bytes())?;

  let mut buffer = Cursor::new(Vec::new());
  document.save(&mut buffer)?;
  Ok(buffer.into_inner())
}
}

Applying a nonexistent style id does not make the document display that style. A robust writer should read the style definitions part, check by styleId, optionally map from style name to id, and either add the missing style or return a clear error. A styles part is optional in a minimal document, so code must handle the missing-part case explicitly.

In ooxmlsdk, generated schema types include Styles, Style, ParagraphProperties, ParagraphStyleId, and StyleRunProperties.