For generating the cache key, to uniquely identify a document file, we use a string combination of file extension, file size and file date, this way cache collisions do not occur and we can reuse the cached file even if the file name before extension is changed (file1.docx and file2.docx have same cache key because it's still the same document according to file extension, file size and file date).

File providers like FileSystemFileProvider (a file on disk, on Amazon S3, on Azure) can provide file size and file date automatically however some file providers will not have this knowledge, e.g.StreamFileProvider, MemoryFileProvider (how could they know date modified of your data in a byte array or a stream?).

So for this purpose, these kind of providers have an additional property or constructor argument named DateModified and/or Size. You need to specify these to ensure you uniquely identify a document.