Thanks MEB,
Yes, ''Show Icon Preview'' is checked, allowing the preview of all my other icons, in any other format.
I can open any document with 'Get Info', but I don't quite understand what you mean by ''set the .afphoto file to Preview'', or what means ''Open with section''.
If you mean that, once in the Get Info menu, I should choose Preview as the 'by default app to open .afphoto files, well I tried, and the Preview app is faded out from the list of apps, so I could not select it.
I will restart my computer anyway, just in case, and will let you know...