I'm currently an intern in a very large company. My internship will end next month, I really like this job and my supervisor wants me to stay for the summer. He made a demand to extend my work contract and a member of the human resources called me and asked me to send my CV and my grades. This is odd, because I already sent them my resume and grades when I first got hired a few months ago. Even if they "lost" my resume or grades, why do they need them?
Because their formal employment process requires them. To be consistent if they require them from external hires they will require them from you.
It may be that the internship prices is entirely separate from the hiring process. This is rather common - disjointed processes across large organisations are the norm.
Or it may be that the HR teams are doing the right thing and not holding copies of your data any longer than they need to. In one of my previous roles, we would discard most copies of candidates CVs, applications etc as soon as we had hired or turned them down.
You have been an intern of that company for a few months now. The resume you sent them before you were hired is not current anymore.
You should update your resume to include your experience with this company to make it current. Then you apply for an extension of the internship contract formally.
I think this is actually a good sign. They must be happy with your performance so far. You should do what they say if you want to continue to work for them.
Some companies/industries require a current resume as part of an employees paperwork. For the industry I'm in this is part of the regulatory paperwork for such things as audits (in our case FDA). It needs to be kept updated every 6 to 12 months.
I got my bachelors in '79 and masters in '83 but I still have to keep updated.