Batch renaming of files based on content/title

I have large folders full of pdf files with arbitrary (actually date-based names) that were produced by a scanner. The pdf files are mainly scientific journal articles that were scanned and then run through OCR. I would like to rename the files with the title found on the first page of the article and do this for multiple files in a batch

For example here is a file name:

2009_03_16_02_36_16.pdf

This is a pdf scan of an article entitled "Effect of blueberry feeding on plasma lipids in pigs".

I would like to have the file renamed as:

Effect of blueberry feeding on plasma lipids in pigs.pdf

I would like to do this for a large number of files in a batch.

If the title is too long it if fine to shorten it by taking only the first x number of words/letters e.g. the first 100 characters of the title. In nearly all the articles the title is on the first page in a large font.

How can I do this?