i'm positive without even googling there are definitely ways to batch composite xls to whatever. i do this with adobe programs all day between file types; i know it's a thing for office programs as well.Can you tell me how to convert 36 excel files in an .xls format to a csv or .XLSX format without opening the file and in a short time? Oh, the files are over 200mb each.
i would google ......okay i did it.
https://www.online-tech-tips.com/computer-tips/how-to-change-file-extension/
there's a few options, one involves cmd prompt and the others third party software. the only issue i would worry about are elements/tables/colors etc not always converting correctly but that can always be an issue.