It would change the tense. have/has + V3 (present perfect tense) is used to refer to event that is already finished by now. Simple past is used to refer to activites that was done in the past. Present perfect sentence isn't usually followed by time (? ). In this case, the word 'have' acts as the english equivalent for malay (and indonesian) word 'telah'. Amir telah menulis kitab. Amir has written a book. Amir menulis kitab kemarin. Amir wrote a book yesterday. For #2, the tense used is past perfect. Past perfect is used to refer to a past event that already ended in the past or preceded another past event. Or simply, "paster" than past event. e.g. I had already known before she confessed. Hope it helps. (:

yes, if you add have then it is the Present Perfect Tense. That is a present tense and always tells us something about now. It describes an action that happened in the past but has consequences in the present or is not finished yet. But if you add 'had' then it is Past Perfect Tense and it describes an action that happened before some other action in the past.