Translation package size

Dear community, 

when I create translation packages for external translation, their size is usually the same as of the original file, therefore emailing doesn´t work for the big ones.

Last week I had a 105 Mb doc, and the package I sent to the agency was 99 Mb. However, when the agency returned the package, it weighed 5 Mb only. How is that possible? 

Thanks in advance!

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