I have a HD apprentice version of houdini.. with NO watermark.
but when I open the file on Escape version(or i don't know which version this is… it is .hip(non non-commercial version at my school) . It gives the watermark.


is it like some kind of bug? or is it supposed to be like this?

Yes, it is supposed to be like this.

Otherwise companies could use cheap noncommercial licenses to create content for use with their commercial licenses.

but the thing is that..

my non commercial HD version doesn't make watermark. (.hipnc)
my school computer doesn't make watermark. (.hip)

but when I transfer my HD version to my school computer.. it makes watermark.

they both are not supposed to make watermark, but it does, when file is transfered.

I think my school computer doesn't recognize my HD version .hipnc file as HD, but just normal non commercial file..

As eetu mentioned, this is the correct behaviour. Any hipnc loaded into a commercial Houdini will begin watermarking all output images. It doesn't matter if it came from the free or HD version; both are non-commercial (the ‘nc’ part of hipnc). Because of this, the commercial Houdini session changes to a non-commercial session, resulting in the watermarking you see. eetu also correctly stated the reason why - so that assets created with inexpensive non-commercial licenses cannot be transferred to commercial ones.

The thing is.. I have never had this problem.. before.
I have done it several time…

My school computer might be non commercial version as well.. but maybe special version..? (it's not education version btw) because it saves file as .hip but if I open .hipnc file.. it asks me if I am sure about opening non commercial version on this..
but it used to not make watermark..

The behavior is expected as the above posters have told you. If you alter a .hip with a .hipnc license of Houdini your file will become a hipnc when you save it.

rob