Anybody knows how to include meta tags to pdf fiels. please suggest.
Seems like a strange question to me, PDF's aren't even native web files, why on earth would they have meta tags?
If you are using the full version of Adobe Acrobat, you can save some meta-information in the "Document Properties" menu item.
If you are using a free document converter from eg Word or OpenOffice, these often pick up the information from File > Properties.
I don't know to what extent search engines look at PDF meta data.