Classic Mac OS (before Mac OS X) stored file type and creator codes in a special place in the filesystem that non-Mac filesystems don’t really have. This info is called the “Finder metadata”. Depending on how those files got to you, that info may or may not have been preserved.
Also note that some common Mac-specific graphics/image file formats for that era stored important information in the “Resource Fork”, which is another place the Mac HFS filesystem could store some of a file’s data, that non-Mac filesystems don’t really have. And again, depending on how these files got packaged up and transferred from the Mac to your Windows PC, that information may or may not have been preserved. This could be a problem if the image was some Mac-specific graphic’s app’s proprietary format, and that developer chose to store important info in the resource fork.
FYI, the part of a classic Mac file that’s the same cross-platform is called the “Data Fork”. So if you have, say, a text or GIF or JPEG file, if all you have is the data fork, you’re still okay. There are ways to discover the type and read the file like any other text or GIF or JPEG file.
If you lost the Finder metadata, no worries, there are other ways to find the file’s type. If you lost the resource forks, depending on how Mac-specific the file format was, you might be stuck. But if these were standard cross-platform file formats, you’re probably okay even without resource forks.