How can I copy files from streamingAssetsPath to persistentDataPath only when changed

I have some files(html and images) in streamAssetPath. Because in Android webview can't read files in streamAssetPath, I copy them to persistentDataPath and read them.
For now I always copy the files when the webview is loaded, and I would like to change it only when the files in the streamAssetPath and the files in the PersistentDataPath are different from each other.
I can read information of files in the persistentDataPath using FileInfo class but I couldn't find the way I can read information of files in streamAssetPath. Is there any way to do it?
Thank you in advance.

 

You could check checksums of the files, if you want to see if they are changed.
http://wiki.unity3d.com/index.php?title=MD5