Technology Apr 26, 2026 · 2 min read

Implementing Bates Numbering in Rust — Stamping Every Page of a Legal Document

All tests run on an 8-year-old MacBook Air. Bates numbering is a sequential stamp applied to every page of a legal document — "EXHIBIT-0001", "EXHIBIT-0002" — so every page can be uniquely referenced in court. It sounds simple. The PDF implementation has a few gotchas. The basic appro...

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DEV Community
by hiyoyo
Implementing Bates Numbering in Rust — Stamping Every Page of a Legal Document

All tests run on an 8-year-old MacBook Air.

Bates numbering is a sequential stamp applied to every page of a legal document — "EXHIBIT-0001", "EXHIBIT-0002" — so every page can be uniquely referenced in court.

It sounds simple. The PDF implementation has a few gotchas.

The basic approach

For each page, inject a text operator into the content stream at a fixed position:

pub fn apply_bates(
    doc: &mut Document,
    prefix: &str,
    start: u32,
    digits: usize,
    position: BatesPosition,
) -> Result<(), lopdf::Error> {
    let pages: Vec = doc.page_iter().collect();

    for (i, page_id) in pages.iter().enumerate() {
        let number = format!("{}{:0>width$}", prefix, start + i as u32, width = digits);
        let (x, y) = position.coordinates_for_page(doc, *page_id);

        let stamp = format!(
            "q BT /HiyokoF1 9 Tf 0 0 0 rg {} {} Td ({}) Tj ET Q\n",
            x, y, number
        );

        append_to_page_content(doc, *page_id, stamp.as_bytes())?;
    }

    Ok(())
}

The font embedding problem

/HiyokoF1 in that content stream references a font resource. If the font isn't in the page's resource dictionary, viewers will substitute or error.

You need to embed a font reference in every page's Resources:

pub fn ensure_font_resource(
    doc: &mut Document,
    page_id: ObjectId,
    font_id: ObjectId,
) -> Result<(), lopdf::Error> {
    let page = doc.get_object_mut(page_id)?.as_dict_mut()?;

    let resources = page
        .get_mut(b"Resources")
        .and_then(|r| r.as_dict_mut())
        .ok_or(lopdf::Error::DictKey)?;

    let fonts = resources
        .entry(b"Font".to_vec())
        .or_insert_with(|| Object::Dictionary(Dictionary::new()))
        .as_dict_mut()?;

    fonts.set(b"HiyokoF1", Object::Reference(font_id));
    Ok(())
}

Miss this step and your stamps are invisible.

Position logic

Bottom-right is the legal standard. But page dimensions vary — A4, Letter, custom sizes — so you can't hardcode coordinates.

pub fn bottom_right(doc: &Document, page_id: ObjectId) -> (f64, f64) {
    let (width, height) = get_page_size(doc, page_id);
    (width - 72.0, 36.0)  // 1-inch from right, 0.5-inch from bottom
}

Result

Prefix, start number, zero-padding width, position — fully configurable. Processes a 500-page document in under a second.

Hiyoko PDF Vault → https://hiyokoko.gumroad.com/l/HiyokoPDFVault
X → @hiyoyok

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This article was originally published by DEV Community and written by hiyoyo.

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