If you work for a large PR firm, is it difficult to be recognized by upper management?

It is never difficult to be recognized. As long as you work hard, be creative, innovative and always show your work, you will be recognized. Even if, it took you a long time but one day you will make it. 

YOU HAVE TO REPORT SOME ONE IN THE LINE MANAGEMENT,,,,,,,,,, WHAT MAKES THE DIFFERENCE IF THE TOP MANAGEMENT D,NT KNOW YOU ? 

Generally, A pressure tactics is the style of Management adopted in large PR Firm, and their recognition will be cantered on a very few, heart-felt impartial recognition is not often received after a certain stage, at the same time you will not be totally ignored, and you may be troubling to find out a solid reason to quit.  This is my personal opinion, views may change with others, that I am not sure about.

absolutely you can, but it not a factor to dealt with !!! just if you are creating a great creative jobs and your team leader makes you down

Who said that , on the contrary , it is very difficult for any organization to ignore or do not give sufficient attention for this impotant function , which is one of  the most  important  factors of  promotional mix , as I answerd in imilar question in the past, the primary objective of public relations is to improve the reputation of the organization constantly towards external audiences as well as to  the internal audiences of organization, through the fulfillment of the obligations of  the company to them, also the social role that can be played PR 

Well i believe that working with the big name is better, Indeed there are many challenges in the big organizations but Life sets us a challenge to test our courage and never forget that Leadership comes from facing and overcoming the challenges, All you have to do is to be consistent in what you are doing and you will see soon that you will get some recognition for your work from the upper management.

The work you do in any organisation would set you apart from the rest and make you noticeable. So working in a small organisation would ensure your survival for a longer time, but in a large organisation the rewards would be high, though the risk is higher. So let your work speak for you. Make a brand out of yourself, and so you do not have to worry about getting noticed and getting recognized.

At all because of public relations in modern management is one of the most important elements of the continuation of the giant companies because it depends on the complexity of relations that will allow the company to expand the largest in its field

your achievements has a voice that can never go unheard :).

Recognition of one's good work comes .............finally irrespective of of the size of the organisation one works for. It also depends on the nature of your job, your line manager's relationship with you and the overall policy of the company in acknowledging success and celebrate it. Besides, one should not be ashamed of promoting oneself if something good for the company has been done through one's efforts. There is a proverb in Punjabi, my mother tongue (translated)....."even a mother doesn't breastfeed her child if s/he doesn't cry):-.