code to create a trial version windows application

If you don't want to depends on system date then you have to choice,

First of all, let me tell you What's logic in software means,

Suppose your developing software for accounting, as we know you can not create bill for past date if your in latest transaction number. e.g.,

invoice no:1 Date: 20/07/16

invoice no:2 Date: 21/07/16

invoice no:3 Date: 22/07/16

invoice no:4 Date: 23/07/16

in this series of invoice no you can not create invoice no 5 with date: 20/07/16 or any other past date, since its against civil low in India.

your invoice no 5 must be greater than or equal to 23/07/16.

so,Even your user try to change system date and try to create invoice, he/she may fail.

you can show warning message and close software immediately.

Another method is to use internet timer,

Find attached copy of module which is in VB.net, convert it to C# if you required.

and use it as follow,

Code to check internet connection,

Import system.net.

You can use both things by merging and using your own logic.