yes, that was my first thought so I re-downloaded it in vein. But, some time later I tried again using another windows account. Then the horse with wings icon appeared and the update ran!
Thank you all for the support.

I tried to install Pmail update version 4.73 but I can't. I get a blue banner: "

This app can't run on your pc". I have W10 Pro 1803. I tried several possible solutions like compatibility settings and smartscreen settings. The German installation could work but that is not what I want.

What's wrong, the w32-473.exe or Windows10 and how to solve?

I have not heard any other reports about that message stating that it won't run on this PC.  The only known issue with Pegasus Mail on Win10 is that it will not function correctly if installed in a \Program Files directory. 

The only suggestion I have is to try again with a fresh download.

The only time I encountered that Windows message was when

the installation file I downloaded (not the PM file though) was corrupted or not

complete. Try to download and check the size of the file. What about your  AV program, has it interfered?

Mungo