Some programs that claim to do many different things with embroidery designs rarely do them all well. There are programs such as Buzz Tools and others that may have limits on the size of zip files they can unzip, extract decompress. Some programs will only unzip files that have embroidery formats in them and ignore other files such as pdf and Word documents. When downloading the zip files always click on "SAVE" and not on "OPEN"
If you use one of these programs and still get invalid file messages I suggest you download a zip program, such as 7zip from 7zip.Org . This is a free program that we use to zip all of our files. We have never had a problem with it.