Hi.

Did you add the code for file upload?

const storage = multer.diskStorage({
  destination: (req, file, cb) => {
    cb(null, "./files");
  },
  filename: (req, file, cb) => {
    cb(null, `${file.fieldname}_${+new Date()}.jpg`);
  }
});
const upload = multer({
  storage
});
...
router.post("/uploadImage", upload.single('upload'), async (req, res, next) => {
  res.json({
    uploaded: true,
    url: `${process.env.BASE_URL}/${req.file.filename}`
  });
});

This is the part that gets file from the file upload request.

On front end, I have:

<CKEditor
  editor={ClassicEditor}
  data={content || ""}
  onInit={editor => {
    if (edit) {
        setContent(doc.document);
    }
  }}
  onChange={(event, editor) => {
  const data = editor.getData();
    setContent(data);
    setDirty(true);
  }}
  config={{
    ckfinder: {
        uploadUrl:
        `${APIURL}/pdf/uploadImage`
    }
  }}
/>

where:

config={{
  ckfinder: {
    uploadUrl:
      `${APIURL}/pdf/uploadImage`
  }
}}

actually does the upload.