"Did you get one of the papers?" "Yes I got one" or "yes I got it"
Here the question is specifically about any one of papers(among all the papers). Hence
"Yes I got one" will be more perfect that
"Yes I got it", since
it referring to a particular paper but
One referring to any one among the all papers.
"I missed one event day" or " I missed an event today"
"Can I have one hamburger, please" or "Can I have a hamburger, please"
In both the above examples using
An will give same meaning and using
An/A based on the Vowels will be more perfect than simply using