for CDS can we prepare only and only from arihant Pathfinder

Arihant's Book is definitely good. You can surely prepare from Pathfinder for CDS By Arihant Experts. But there are other books also you can use for prepare from. For English language and Vocabulary, you can rely on Wren & Martins High School English Grammar & Composition or Word Power Made Easy by Norman Lewis. For general knowledge, Arihant's book is good. You can also prepare from Manorama Year Book. Also read newspapers daily for staying updated regarding current affairs. For Mathematics- Mathematics for CDS preparation by RS Aggarwal or Pathfinder for CDS by Arihant's. Both the books are great. For basics, you can start with your class 5 to 10 maths books. Don't go for a huge number of books, the syllabus is simple so you can prepare from simple books and then give mock tests and solve previous few years' exam papers to boost your preparation.