Hi,
If you wrap your script in the preSign event in an if statement, which first checks the application version.
if (app.viewerVersion >= 9)
{
//your script here
}
If the user has Reader 8 then the script will not run.
If you are going to have an alternative approach in a different event for users with Reader 8, then a similar approach would work in that different event:
if (app.viewerVersion < 9)
{
//your alternative script here
}
Hope that helps,
Niall