A more comprehensive answer:
If you want to check the existence of a local file before performing some task, here is the comprehensive snippet:
- name: get file stat to be able to perform a check in the following task
local_action: stat path=/path/to/file
register: file
- name: copy file if it exists
copy: src=/path/to/file dest=/destination/path
when: file.stat.exists
If you want to check the existence of a remote file before performing some task, this is the way to go:
- name: get file stat to be able to perform check in the following task
stat: path=/path/to/file
register: file
- name: copy file if it exists
copy: src=/path/to/file dest=/destination/path
when: file.stat.exists