How to make database in pendrive for desktop application?

@abhishek Whenever any application executes, it holds a specific memory at RAM, any resources used by your application (while de-atached the external media) will be unavailable. If you still want to stand on the safer side then you can use drive disconnected events and close your application based on the event. https://www.codeproject.com/Articles/18062/Detecting-USB-Drive-Removal-in-a-C-Program

In addition to my earlier post, if you use .net core with standalone publishing method then you don't even require any runtime to be installed on the target machine (your application behaves like plug n play architecture) otherwise you have to install .net framework

If you put all your reference DLLs with your executable then your application will be portable and can work on pen drives too, regarding databases, you can opt db likes msaccess, sqlite. However, I am not quite sure about sql (I haven't tried but I believe that when you attach your mdf file (located on your pen drive) it might work.