when i try to place order manually(impersonate) there is no option to add a product to the cart.

i don`t know if is bug or a feature.. if you as the store admin want to place order manually, then do you have to login with the customer user?

You just click "Place order" button on the customer details page (admin area). Once you're redirected to public store as an impersonated customer, add required products to the cart and place an order. I presume that you do not see "add to cart" button because your customer doesn't have this permission. Go to admin area > configuration > access control list and ensure this customer has "Public store. Enable shopping cart" permission

thanks!
the option "Public store. Display Prices" has to be enabled also.