You must be missing something a SQL Server database comes as MDF and LDF or .BAKs which could be in .zip or .rar or MSI files but not PDF file. PDF files are text files so you need to check Codeplex for a new download.
http://www.codeplex.com/MSFTDBProdSamples/Release/ProjectReleases.aspx?ReleaseId=4004
Kind regards,
Gift Peddie