The BOM is a byte sequence that identifies the document as UTF16 and is prepended to the file contents.
in reply to Re^2: Mixed character encoding issues
in thread Mixed character encoding issues
I am under the impression that MS documents (Excel,Word) contain this sequence not on the beginning of the file but somewhere later because they reserve the first few bytes for their header information.(They even write a BOM for UTF8 too,which sucks of course)
Because the document and BOM can be UTF16 LE or BE,Encode does need to understand what kind it is. Check this Stackoveflow answer by brian d foy.
However to simplify the process and save you from the trouble with excel,I would suggest that you open the excel file and export the data as UTF8 text or CSV file. Then you
can use your Perl parser/module of choice to get to the contents