How to print tamil font in dotmatrix printer using VB.Net code

nope, dot matrix printer is different.

Check what your printer can do. You do not even tell us which printer, most dot matrix printers use the Epson command sequences and capabilities.

So, first get the manual for the printer and check if fonts can be downloaded, if so use that method. If not then you will need to turn the page into an graphic and use the printer command language to print it as a graphic, painfully slow printing but it will work.