Is there any restrictions to apply PR in Singapore? And I need to know the important papers required to apply permanent resident in Singapore and suggest me simple ways to do that.

http://www.ica.gov.sg/page.aspx?pageid=151

Permanent Resident Application (http://www.mfa.gov.sg/content/mfa/overseasmission/doha/consular_services/pr_application.html)

This is not the same as citizenship of course.