Sharepoint provides a very powerful OOTB advanced search web part. However if you want to add custom property to appear in property restiction, it is quite easy!!!
Create a refinable property for custom property which you want to be displayed in property restriction.
Now go to the Advanced search web part page and edit the advanced search web part. Under the properties section, click on Properties and edit.
Copy text in “Properties” text box in this section and paste it into notepad editor.Suppose we want to add property named “DocsDepartment”, add PropertyDef named “DocsDepartment” and add PreopertyRef “DocsDepartment” in all result type as follows: