Not all previously installed software survives. A prime example is most antivirus systems. Those do not survive (not should they) an OS upgrade. There are likely others like these as well.
This is why over and over it's advised to backup what you can't lose and prepare to reinstall or replace apps.
C/net has free upgrade information from Windows 7 to Windows 10, because of the end of support for 7. If you use this link to upgrade will it require me to manually re-install all my added software? Or does the upgrade automatically carry over my previously installed software? Thanks for any info.