The spec for this action:
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G11.2111850
An example of a form using this action:
https://www2.illinois.gov/rev/forms/reg/Documents/reg-1-mr.pdf
const obj = this._catDict.getRaw("PageLabels");
    if (!obj) {
      return null;
    }
    const pageLabels = new Array(this.numPages);
    let style = null,
      prefix = "";
    const numberTree = new NumberTree(obj, this.xref);
    const nums = numberTree.getAll();
    let currentLabel = "",
      currentIndex = 1;
    for (let i = 0, ii = this.numPages; i < ii; i++) {
      const labelDict = nums.get(i);
      if (labelDict !== undefined) {
        if (!isDict(labelDict)) {
          throw new FormatError("PageLabel is not a dictionary.");
        }
        if (
          labelDict.has("Type") &&
          !isName(labelDict.get("Type"), "PageLabel")
        ) {
          throw new FormatError("Invalid type in PageLabel dictionary.");
        }
        if (labelDict.has("S")) {
          const s = labelDict.get("S");
          if (!isName(s)) {
            throw new FormatError("Invalid style in PageLabel dictionary.");
          }
          style = s.name;