Open Source Document Management System | OpenKM

You are talking about OS file system properties ?

Well, little explanation. From browser point of view, will be a security break if you will be able to access this kind of OS information. That means from browser layer will not be possible. The only way for doing it should be creating a small application at OS level for it ( might be with JAVA, .NET are two great candidates ). Also in your case should be necessary small code change to create a new method at REST layer for it.

You can apply the same keyword selecting several documents and then using the contextual menu. I do not know if it might help you in some way? Otherwise, you should build your own UI for it.

Also, I do not suggest using keywords for it, I suggest use metadata rather than keywords for performance and other reasons that will be so long to explain. Basically, create a field definition into metadata for storing keywords rather what are you doing now. With metadata, you have the same option for adding fields or updating to several nodes.

Take a look here:
https://docs.openkm.com/kcenter/view/ok ... adata.html