If you are using curl or some terminal command, & has a special meaning there. Try gettig it inside quotes as
curl 'http://localhost/pdf/123?option=456&clientId=789'
This code is working:
app.get('/pdf/:id', function(req, res) { console.log(req.params); console.log(req.query); res.end();});
Output:
[ id: '123' ]{ option: '456', clientId: '789' }GET /pdf/123?option=456&clientId=789 200 1ms