generating graph using excel values

You can implement both Excel and Word functionality using Open XML SDK:
http://www.microsoft.com/en-us/download/details.aspx?id=30425[^].

This way, you can support new XML-based Office formats (such as .DOCX, .XLSX), ECMA-376 standard:
http://en.wikipedia.org/wiki/Microsoft_Office_XML_formats[^],
http://en.wikipedia.org/wiki/Office_Open_XML[^].

This way, you can work without Office installed. Also, the documents are supported by 3rd-party software. Please see my past answers:
Convert Office-Documents to PDF without interop[^],
Need a rather unique WPF text editor control[^],
Hi how can i display word file in windows application using c#.net[^],
Read a word file without using Interop.word dll...Do not want to install word in IIS..[^].

This is another option: http://npoi.codeplex.com/[^].

Another option is to use Office Interop assemblies, but it will require installed Office components on the target computer.

And, finally, when you manage to get data from Office documents, you can map it onto PDF structure. To produce PDF itself, you can really use the .NET port of iText; this port is called iTextSharp:
http://en.wikipedia.org/wiki/IText[^],
http://itextpdf.com/[^],
http://sourceforge.net/projects/itextsharp/[^].

I provided links to iText, too, because nearly all documentation you need to work with iTextSharp is there, provided as Java documentation.

—SA