When you install windows over the top - unless you tell it to format the drive, then all the documents settings etc will copied to the new system under windows old.

Pdo.exe is an either or programme sometimes it is a virus and sometimes not depending on the location - temp file area is bad but, it is also an unpacking area for installations

The detection in system restore shows that a reformat was not done prior to the install

The alerts were probably malware signatures held in memory by your AV/Am software