Hi Isamu, There isn't any malware/virus scans on the uploaded filedocuments within Mendix. We've also encountered that issue and created the Virus Scan 4 Mendix module to check the content. The module can be downloaded from the appstore. Beside that there is an example project of the module and read the detail blog on how to use the module.
I hope this will answer your question!
Mendiix does not check your filedocuments. If you want to check those files there is an app for that: https://appstore.home.mendix.com/link/app/29130/Appronto/Virus-Scan-4-Mendix
The assumption is that it is the responsability of the user. And if there is an virus in a document you can easily track who has uploaded that one.