If you are looking for documents on the internet , you ‘d rather use specialized search engines which will bring you documents with indicated extensions such as word , pdf , ppt .Here is a compilation of the best document search engines I found online :
1- DocJax


Use this search engine to find documents in the following ‘Documents Sharing Communities’

3-Find a PDF
Search PDF Files Easily and Quickly

4 – PDFfind
Search only PDF files online

5 – Brupt
Document Search Engine based on Google Customized Search.

6- 09h15
Search engine in various languages for documents , pdf , presentations and spreadsheets.

7- TypePDF
Searches through “1045691” of PDF documents and ebooks found in the world wide web.

8 –FreeBookSearch
This search will find documents on school, college and university websites .

9 – Osun
Searches for doc , pdf and ppt

10 – PDF Search Engine
Searches for documents with the following extensions : doc , pdf , chm , rft , txt

Please feel free to suggest more links to document search engines .