What version of Acrobat are you using?
If you're using the Windows version, you can use ADBC (Adobe DataBase Connectivity) to connect a form to a spreadsheet, but there are a number of issues and you have to learn about ADBC, which was removed form Acrobat 10. For more information, see: http://livedocs.adobe.com/acrobat_sdk/9.1/Acrobat9_1_HTMLHelp/JS_Dev_Databases.84.2.html
The following article at the pay site pdfscripting.com will get you up to speed quickly: http://www.pdfscripting.com/members/login.cfm?hpage=150.cfm
Otherwise, you'll have to search around for info on how to do this. It's also possible, and maybe easier, with an XFA form created with LiveCycle Designer, but you should ask in the Designer forum here for more info.