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.
PDFViewerApplication.rotatePages(-90);
}
function webViewerOptionalContentConfig(evt) {
  PDFViewerApplication.pdfViewer.optionalContentConfigPromise = evt.promise;
}
function webViewerSwitchScrollMode(evt) {
  PDFViewerApplication.pdfViewer.scrollMode = evt.mode;
}
function webViewerSwitchSpreadMode(evt) {
  PDFViewerApplication.pdfViewer.spreadMode = evt.mode;
}
function webViewerDocumentProperties() {
  PDFViewerApplication.pdfDocumentProperties.open();
}
function webViewerFindFromUrlHash(evt) {
  PDFViewerApplication.eventBus.dispatch("find", {
    source: evt.source,
    type: "",
    query: evt.query,
    phraseSearch: evt.phraseSearch,
    caseSensitive: false,
    entireWord: false,
    highlightAll: true,
    findPrevious: false,
    matchDiacritics: true,
  });
}
function webViewerUpdateFindMatchesCount({ matchesCount }) {