I know that Company name should not be translated, but LTD or Ltd. should be translated? Just for example, Apple Ltd.
This seems like an odd question for ELL. "Ltd." is already English ("Limited"), so it doesn't need translation.
However, in a more general case, if the company is incorporated in a particular country, then you should use the incorporation designation from that country, untranslated. For example, there is a large international bank headquartered in Spain that is referred to as Banco Santander, S.A. in English-language articles, even though "S.A." stands for the Spanish phrase "Sociedad Anónima."
This is, however, confused by the fact that multinational companies often have wholly-owned subsidiaries that are locally incorporated. There is an entity headquartered in Boston that is called Santander Bank, N.A. (where "N.A." stands for "National Association"). It is the wholly-owned subsidiary of Banco Santander, S.A. that conducts the parent company's business within the United States.