https://github.com/mozilla/pdf.js/blob/0df1a5661958df0c4ed2f73b0f3266d825c5c280/src/display/api.js#L710-L719
The return type signature `@returns {Promise<{num: number, gen: number}>}` is mismatched with its definition. (should be `@returns {Promise<number>}`)
this.pagePromises[pageIndex] = promise;
    return promise;
  }
  getPageIndex(ref) {
    return this.messageHandler
      .sendWithPromise("GetPageIndex", {
        ref,
      })
      .catch(function (reason) {
        return Promise.reject(new Error(reason));
      });
  }
  getAnnotations(pageIndex, intent) {
    return this.messageHandler.sendWithPromise("GetAnnotations", {
      pageIndex,
      intent,
    });
  }
  saveDocument() {
    return this.messageHandler
      .sendWithPromise("SaveDocument", {
        numPages: this._numPages,
        annotationStorage: this.annotationStorage.serializable,
        filename: this._fullReader?.filename ?? null,
      })
      .finally(() => {
        this.annotationStorage.resetModified();
      });
  }
  getFieldObjects() {