If you want to use any public documents in latvia, that originates from United States, you must get APOSTIL or legalisation from U.S. See ministry of foreign affairs advise for foreigners: http://www.am.gov.lv/en/service/legalisation/
Hope this information helps you
If you ever need legalization in Russia have a look at this link http://www.alba-translating.ru/index.php/eng/apostille.html
Useful link about apostille in Ukraine http://www.apostille.ua
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