Saving in HTML5 is available only for Display banners.

https://lh5.googleusercontent.com/xepUp7KWEMVPUFNzO03WW75TMR9Wax5cg1-iDQMG-XUA73m0b6TfPbn5nJLyxBaYHmudSIdRK7KQreGNQOyC8Sm3zd24LKe6uj3kN27aSrW0HVAm1yqn6-YojlrpCOy9ANPwOzOb8NLSJuovv6wvYHKQThOM2eXftCa4k6isRG_hbUiJ6-KNuKaTlw

To download the creative in HTML5:

1. Open the creative.
2. Click on the Download button in the top right corner.
3. Click on the HTML5 button.
4. Choose the Ad network for which you want to optimize.
5. Now all sizes are optimized for the chosen network.
6. Click on the Download button below in the menu
7. The file creation may take from a few seconds to several minutes.
8. When the file is ready, the message "HTML export is ready" will briefly appear above the creative.
9. Check the counter on the bell in the upper right corner. This is the notification bar where you can see all of your ready downloads. If there is a new value, the file is ready for download.

To download the specific size of the project in HTML5:

1. Open the creative.
2. Open the size you want to download.