My server has a static IP and listens to a port (8000) when it get's a file it automatically saves it with predefined extension. It's an internal project and no one knows about this server. I see few HTTP1.0/1.1 requests a day. should I be worried? They're origin is in Russia, Viet Nam and may be more.
It's an internal project and no one knows about this server.
Just because you did not tell anybody does not mean that nobody knows about it. Any host exposed to the internet is usually often checked for the kind of services if provides. Also the usual exploits are tried in the hope to find an easy target to take over and misuse, i.e. sending spam, delivering malware, attacking other systems within a DDoS attack, cryptomining, etc.
... should I be worried?
If your server is not secure you should be worried. It is better to keep the attack surface small, for example by requiring authentication, limiting access to specific IP addresses or whatever is possible in your specific use case.