The 'Save to File' (i.e. floppy icon) is grayed out, if you sent a function, procedure, package from the DB Explorer to the Editor. Accessing the 'Save to File' and 'Save to File As' by doing a 'right-click | File' are also grayed out.
When editing an existing object's code, you need to click 'Save to DB (Ctrl+S)' button.
To enable the 'Save to File' feature, click on the 'Generate DDL Script' button (i.e. 'SQL' icon). This will display the SQL script in a separate window for the same Editor.
Enhancement request ST5305 has been submitted to Development for consideration in a future release of SQL Navigator.