what is NDA

Hello Unreal,
I have a very strong reason for creating this thread and I want to ask what exactly NDA means.

My situation:

I have been working with a person on a specific project from February 2013- February 2014. Now in this time period I was never asked to sign any NDA, but later on January 2015 he made me sign a general NDA which says nothing about the last project and even the time frame that I have worked for.
Apart from this I was regularly contacted via his personal mail id when I was in contract.

I have some basic questions here:

  1. Do you sign a NDA after a year you complete a project.

  2. When an employee and employer share official documents like NDA, should they use their personal email address.

  3. NDA specifies the art and the time period of the project.

  4. If my contractor is acting as the middle man between the me and the main company, then he should be having both the NDA from his company and the company’s art he has been outsourcing signed by me.

Unfortunately Unreal moderators have kept some of images down and I want to know how long this will be blocked.

Please advice me.
I have supportive documents which I can show if situation requires.
Thanks,
Kauhsik Saha