PHP Web app - Search PDF documents

Hi,

I'm interesting in building a web app which allows users to login to a database and search for PDF files / documents for important information.

Web App
- An online database which holds a collection of 1000s of pdf documents (OCR'd)
- 500 users logins
- UI search function - to find documents and information
- Save, exports functions of the documents etc

The web app with let users search for important information and documents like the WestlawNext web app

This link provides info on how WestlawNext searches PDF documents:
[URL visible pour les membres Pro]

Search Function:

Here's an excerpt of how terms and connectors works in searching for text on westlaw (which is what I'd what to accomplish.):

The Terms and Connectors search method allows you to enter a query that consists of key terms from your issue and connectors specifying the relationship between those terms. For example, you can specify that your terms appear in the same sentence (/s) or the same paragraph (/p).

Please quote for just desktop / laptop version of the web app and a responsive version of the web-app.