On the Mac (Apple products, iOS, iPad, etc.), file extensions aren't necessary to identify the type of a file. For Windows (Microsoft products), its still necessary, though usually hidden these days. A file extension is historically a dot and three letters tacked onto the end of the filename.
For most websites that support uploading and processing files of any type, its much simpler to identify the type of file by examining its file extension (if it has one). Very few websites have the necessary, and more complicated code to do so without it.
Although I use a Mac myself, I'm personally unfamiliar with the iPad specifically. I don't know if you have the ability to rename a file and give it an extension, if it doesn't already have one.