Disabling creation of Multi-File documents

Multi-file documents are a core feature of M-Files so it's not possible to completely disable their use as far as I know. May I ask what is the issue you are dealing with? New M-Files users may need some training to grasp the concept, see for instance this discussion on some thoughts on the topic.

is it possibility to deny a multi-file conversion option in a specific class or workflow? document history is a very important in some cases for us, and it disappears if document are converted to multi-file, or is it any way to restore the multi-file to separate documents with the history? 

Conversion to a multi-file document should not remove anything from the version history, it should just create a new document version like this:

What is the behavior like in your vault? Is it possible that there are for instance some event handlers that would modify the version history?

When several documents are converted to a single multi-file

Ah, that's a bit different case. Version history is always specific to a document object, so if your document ID changes (like in your case when copying files to a multi-file document) then you'll lose the version history from the original doc. You may want to consider using document collections for related documents instead of combining docs to a single multi-file document, that way each document's version history is preserved.

Yes, I know the possibilities of the document collection, but my question...according to my understanding, this option cannot be blocked or converted documents cannot be restored without backup procedures. This is ok, I just want to know if there is any way. Thank you.  

There's no built-in configuration option to prevent these operations, but it might be possible to come up with a custom solution (e.g. event handlers and/or UI extensions). These would require some development effort. If this is a major issue for you, I suggest raising this with your M-Files representative.

There's no built-in configuration option to prevent these operations, but it might be possible to come up with a custom solution (e.g. event handlers and/or UI extensions). These would require some development effort. If this is a major issue for you, I suggest raising this with your M-Files representative.