I have found many posts where solutions to read PDFs has been proposed. I want to read a PDF file word by word and do some processing on it. people suggest pdfMiner which converts entire PDF file into text file. But what i want is that to read PDFs word by word. Can anyone suggest a library that does this?
I'm using pdfminer and it is an excellent lib especially if you're comfortable programming in python. It reads PDF and extracts every character, and it provides its bounding box as a tuple (x0,y0,x1,y1). Pdfminer will extract rectangles, lines and some images, and will try to detect words. It has an unpleasant O(N^3) routine that analyses bounding boxes to coalesce them, so it can get very slow on some files. Try to convert your typical file - maybe it'll be fast for you, or maybe it'll take 1 hour, depends on the file.
You can easily dump a pdf out as text, that's the first thing you should try for your application. You can also dump XML (see below), but you can't modify PDF. XML is the most complete representation of the PDF you can get out of it.
You have to read through the examples to use it in your python code, it doesn't have much documentation. 
The example that comes with PdfMiner that transforms PDF into xml shows best how to use the lib in your code. It also shows you what's extracted in human-readable (as far as xml goes) form.
You can call it with parameters that tell it to "analyze" the pdf. If you do, it'll coalesce letters into blocks of text (words and sentences; sentences will have spaces so it's easy to tokenize into words in python).
Python to read PDF files