The admit card for Combined Defence Service Examination (I) 2018 can be found at the Union Public Service Commission’s (UPSC) official website. 

Simple steps to download UPSC CDS Exam (I) 2018 Admit Card as follows: 
Step 1: Visit www.upsc.nic.in. 
Step 2: Click on e-admit card: Combined Defence Service Examination (I) 2018 option
Step 3: Enter the required information and submit.
Step 4: Download and print admit card.

About UPSC
Under Article 320 of the Constitution of India, the UPSC is, inter-alia, required to be consulted on all matters relating to recruitment to civil services and posts. The functions of the Commission under Article 320 of the Constitution are:

Conduct examinations for appointment to the services of the Union.
Direct recruitment by selection through interviews.
Appointment of officers on promotion / deputation / absorption.
Framing and amendment of Recruitment Rules for various services and posts under the Government.
Disciplinary cases relating to different Civil Services.
Advising the Government on any matter referred to the Commission by the President of India.

Note: 
The admit cards would be available for download till February 4, 2018.