Using a document management "system" can be quite complex and fairly simple as well. The first element is to properly mark and identify all of your documents to (1) facilitate quick identification, (2) preclude alteration, and (3) ensure that the document is used consistent with your intent. This is most easily done by using a document marking program such as http://www.stampit4word.com/word-document-management.html. This program can mark paper as well as PDF. In many cases your PDF will also let you insert Meta data (other information about your document that is searchable). Using any one of numbe of search engines will allow you to manage your document give a reasonable folder structure.