What are you trying to read these documents with? Use the camera icon to post a screenshot of what you are seeing.
OS X already has fonts for Bangla, called Bangla and Bangla Sangam. What happens if you select the text and switch the font to one of those?
MS Word for Mac does not support Indic scripts, so best to use something else like Text Edit, Pages, or OpenOffice.
PS If nothing works, send me an example of one of your documents (tom at bluesky dot org).