99% of the time this error is because the file isn't really a .indd file (somebody changed the extension). The other 1% usually turn out to be corrupt files.
How large does Windows say the file is?
Open the file in Notepad (it will look like gibberish) if you can and past the first few lines here so we can read the header information.
I did what you told me and here are the 15 lines
PK ti±FËv‰+ + mimetypeapplication/vnd.adobe.indesign-idml-packagePK ti±F7Õsaú AA
–’lmª’¡¨‡mÍÊ3%?GY? klo’JmA$(1¦ =Öžæg$UÉa@N¹íuþÉü’tƒ/P"mÓ¶6ãõ » À×@¿@‚ý·7sß¸¦"ô8ÛnX¯š
ƒ2›; ›n7Îß ü~«a„’0‡øœÑíÆ‚†·o^öß Ï ÆÂ Z ÉE ¿ nGsÊdÃ ”8T\¤ o`Ç.%2 tLåv£ÕÝl àNdÃ]ïUóëV§óÛ†}ï%½ €…¯=gt `fR ¯M“…¯ˆÃ'ô•Íçæ
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OK, that looks like a .idml file. How large is it?
Ok 160 KB
The file has about 12 pages It is a college work
I suspect it's corrupt. Have you tried opening it on another computer?
If I try but I get the same error
I think it's damaged and I don't know any tools that can repair damaged IDML files.
Do you have the original .indd file someplace?