Unicode must be actively supported by applications. If an application fully supports Unicode, you can insert all Unicode characters with PopChar.
Some legacy applications (such as AppleWorks and older versions of Microsoft Word) support only the older "MacRoman" encoding. This means that you can use only a small subset of the Unicode repertoire.
To see which characters can be used in such applications, select "MacRoman" from the pop-up at the right side of the PopChar window.