Will iPhone restoration back to older iOS initialize all settings, apps and so on?

Will iPhone restoration back to older iOS initialize all settings, apps and so on?

I have an iPhone with iOS 10 but want to get this back to iOS 9.3.2.

I already downloaded an .ipsw file for the OS and ready to restore.

The button I would click says ‘initialize iPhone’ in Korean; don’t know what this exactly says in English… It’s on the right side of ‘check updates’, beneath the text ‘iOS 10.0.2’ and ‘iPhone software is up to date’.

After clicking that ‘initialize iPhone’ holding alt-option key, iTune prompts message ‘iTunes will delete iPhone and restore with iOS 9.3.2 …’

I don’t want all my date in the phone lost. May I restore it?