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.get("OpenAction");
    const openAction = Object.create(null);
    if (isDict(obj)) {
      
      
      const destDict = new Dict(this.xref);
      destDict.set("A", obj);
      const resultObj = { url: null, dest: null, action: null };
      Catalog.parseDestDictionary({ destDict, resultObj });
      if (Array.isArray(resultObj.dest)) {
        openAction.dest = resultObj.dest;
      } else if (resultObj.action) {
        openAction.action = resultObj.action;
      }
    } else if (Array.isArray(obj)) {
      openAction.dest = obj;
    }
    return shadow(
      this,
      "openAction",
      objectSize(openAction) > 0 ? openAction : null
    );
  }
  get attachments() {