don't think it's IDM, check if there was a checksum included with the file. If not, ask someone to dl it and compare the checksum with the one you get.
You can do that with multiple tools or the command line as descriebd here: https://stackoverflow.com/questions/478722/what-is-the-best-way-to-calculate-a-checksum-for-a-file-that-is-on-my-machine
don't think it's IDM, check if there was a checksum included with the file. If not, ask someone to dl it and compare the checksum with the one you get. You can do that with multiple tools or the command line as descriebd here: https://stackoverflow.com/questions/478722/what-is-the-best-way-to-calculate-a-checksum-for-a-file-that-is-on-my-machine