We have windows 10 and use the Windows Mail App that comes with it to do our emails.
When clicking on the Send To Email button pdf24 tells us that there is no default email program.
In all the settings in the control panel Windows Mail is the default. Clicking on any email link on websites or documents opens the windows mail, but yours doesn't.
We used to have a free trial of outlook and it worked then, but the trial has now ended and outlook has been uninstalled. Don't really want to spend £120 to buy outlook when we can send emails from everything else.
We have even tried a yahoo mail app which we can set as default and open links etc form everywhere, but again your software says no email program.
The problem can be the X86 X64 mismatch. PDF24 is X86 and and it can be that you mail program does not install an x86 version of the MAPI.dll file, so that the PDF24 Creator can't load that dll.
You could for instance install Thunderbird (it's free) and that should work together with PDF24. If thunderbird x64 does not work then you can try Thunderbird x86.