On Thu, 2021-11-25 at 01:56 +0900, DaeHyun Sung wrote: > It is zipped Compound File Binary Format. So, I added read & check > zipped format I downloaded the attachment and I don't think its zipped (unzip -l fails to show any structure), I think its just a Compound File Binary Format (like the older msoffice file formats) where "gsf list filename" does show its structure. writerfilter/source/filter/WriterFilter.cxx:260 might be closer to what you want, there a oox::ole::OleStorage is created from an XInputStream, like you have in your case, and its ::isStorage should return true if the file is a CFBF.