Custom properties disappeared after print save

When you print a PDF file to a PDF printer you're creating a completely new file, without any of the meta-objects that exist in the old one, such as metadata, form fields, comments, bookmarks, links, layers, etc.

As mentioned, this is considered bad practice, and there are better (and faster) ways of achieving what you're trying to do.

So you should "flatten" the comments and Save. Not print. This will be faster and leave all metadata untouched.

To flatten you can use a Preflight fixup or the "Flatten" plugin which is one of this free tools:

https://www.abracadabrapdf.net/utilitaires/utilities-in-english/abracadabratools_en/

"When my friend click print and save as pdf then these custom properties are removed in new pdf document. why?"

Because this is not a good practice.

Since he uses Acrobat Pro he should use : File menu : Save As (or Save).