So copy factory.php from where it is located and place it into the necessary location.

The problem is in the plugin code. the correct path is: C:\inetpub\wwwroot\administrator\components\com_content\helper not helpers

Correcting this problem causes another error; Fatal error: Cannot redeclare class DocmanFactory in C:\inetpub\wwwroot\administrator\components\com_content\helper\factory.php on line 17

How does one fix that?

How did you manually correct this to make it work?