I have a text document (word or pdf) which has a long list of works cited. How can the works cited be export to bibtex or endnote?
You are spoilt for choice. Google for "reference metadata extraction" and start clicking.
There's free software to extract from PDFs: see Metadata Extraction Tool.
If you have a Word 2007 file, that has (at last) a standardised representation of reflist entries, and EndNote can extract reliably from it.
If you just want to see the citations in an article, RefRuns is a useful tool, and has a simple web interface.