We could use:
https://github.com/mozilla/pdf.js/blob/c3d08580627471432a6ad0b2fdb948df64126afa/src/display/api.js#L929

and look at bit 4.

The following pdf:
https://orimi.com/pdf-test.pdf
is not editable in neither Acrobat nor Edge nor Foxit and nor Okular.
return !!this._scriptingManager;
  }
  /**
   * @type {number}
   */
  get currentPageNumber() {
    return this._currentPageNumber;
  }
  /**
   * @param {number} val - The page number.
   */
  set currentPageNumber(val) {
    if (!Number.isInteger(val)) {
      throw new Error("Invalid page number.");
    }
    if (!this.pdfDocument) {
      return;
    }
    
    if (!this._setCurrentPageNumber(val,  true)) {
      console.error(`currentPageNumber: "${val}" is not a valid page.`);
    }
  }
  /**
   * @returns {boolean} Whether the pageNumber is valid (within bounds).
   * @private
   */
  _setCurrentPageNumber(val, resetCurrentPageView = false) {