The PDF you find might be:
Recent editions of the book (published by Bharati Bhawan Publishers) have improved significantly. They often come with a separate solutions booklet or detailed hints. If you own an older copy, it is worth checking a bookstore or online retailer for the latest edition which may include the official solution key.
Good luck with your JEE preparation.
Here lies the Achilles' heel of an otherwise perfect book. For a typical problem:
Navigating IIT Mathematics: A Guide to A. Das Gupta’s Problems Plus
You don't need a solutions PDF. You need a strategy. Here is a 90-day plan to conquer Das Gupta: