it sounds like your user has already reset IE previously which has disabled to PDF Reader Acitve X addon in ie. To enable it and allow the user to open pdf documents insitu (or according to their Adobe Reader preferences (Start>Adobe Reader>Edit Preferences>Use browser to open pdf documents)
go Tools>Manage Addons>Show All addons.... find the PDF document reader application you are using in the list (usually Adobe PDF) and enable it (click the Enable button)... Close and restart IE for the full changes to take affect.
If the user is continually having to reset the browser... DO NOT enable any other addons until you have identified which ones are causing the problem. (Start>Event Viewer to view the windows logs.)
Once you have identified the root cause of the problem from Event viewer, (probably an Toolbar or bho (Browser Helper Object), you can then use the Programs and Features control panel to uninstall the offending addon. (<sic> an old version of the google toolbar).
You can use Group Policy management to allow only authorised addons to be installed into the browser. Using group policy to manage the users IE registry settings is preferable to using a registry script to customize the IEReset button.
To reset the Internet Explorer settings, saving the following command line as a .bat file to have a check. We will need to press a "Reset" button to reset the settings. I hope this will meet your needs.
"start RunDll32.exe InetCpl.cpl,ResetIEtoDefaults"