Clarification: Your paternal grandfather is still alive and in his 90s now. If so . .
. Don't post a new question in Y! A Genealogy with any living person's name (despite many such postings here and TV programs on searching for living people.) You could not request and pay for a copy of his birth certificate.
That request would have to come from him, since he is still alive. The adoption records from when your grandfather was adopted probably still exist, but are sealed, meaning they are not available for his or your research, meaning they are not available to public inspection (like inspection by your grandfather or you.) This page on Adoption from the Rootsweb.com Guide to Tracing Family Trees explains a bit of the history of sealed adoption records: http://rwguide.rootsweb.ancestry.com/les... The page also gives links to information on researching an adoption. Be sure to click on them and read everything.
Adoptees can legally petition to obtain access to some (if not all) of their adoption records. The laws vary from state to state. See the information here: http://www.childwelfare.gov/systemwide/l... It would have to be something your paternal grandfather would have to do legally, possibly hiring (paying for) a family law attorney to do the legal work.
This eHow.com article outlines the steps to follow for an adoptee (that would be your grandfather) to legally obtain access to his adoption records. Others have given you good information regarding the birth certificate of an adopted child not necessarily bearing information with the birth parents' names. You and your grandfather will have to decide if it is worth his time and money and your time to pursue the research and legal actions.
My personal feeling: Your grandfather's adoptive parents were the ones who loved and cared for him. All of their relatives were also his loving, caring relatives. Even though there may be issues of DNA and ethnic ancestry of his birth parents, including medical/health issues, your grandfather's "true" family was the one he was adopted into with the parents who made the effort to adopt him and raise him.
He's a beloved grandfather for you.
You start with your birth certificate. Then go to the birth/marriage/death certificates of your parents, their parents, their parent, and so on, one generation at a time. All parents are "birth parents"; that means there is no such thing as "birth parents", as one gave birth to you, the other caused her to give birth.
How far records go back depends upon YOUR definition of records. Historical records exist for Charlemagne & Julius Caesar, as well as Nefertiti, so quite some time ago. Most people will not be included in those records, so it is a matter of how far back they go for your ancestors.
Those folks who adopted your paternal grandfather are not relatives; searching info on them is good only to the extent of finding out who your grandfather's parents were. 75 years ago would mean that his records are available in the historical records collections of the State Library where he was born. So, yes, his records are there; it is a matter of whether or not the adoption records give his parents' names.
If you already have their names, then no sweat.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.