Currently using Adobe Reader 9.4.1 on Windows XP Pro and 7 Pro. I would want to deploy version 10 (through Windows Server 2003 GPO) to approximately 50 computers. I've downloaded the MSI file (AdbeRdr1000_en_US.msi) from ftp://ftp.adobe.com/pub/adobe/reader/win/10.x/10.0.0/en_US
If I install Reader version 10, will it automatically uninstall version 9 or will I end up with 2 Reader versions (v9 and v10)?
By default new Reader will try to uninstall older version.
However, if uninstall is not successful, new version will try to install itself anyway. This may lead to unforeseen issues.
I would recommend to configure your GPO to first uninstall existing Reader and, if successful, install new one.
Good to know that version 10 will auto uninstall version 9. If I uninstall version 9 (through GPO) then deploy version 10, users will be left without PDF reader for a few hours or days. I think it's better to have the new version installed regardless of older version removal failure.