What is the difference between view only and read persmission in sharepoint ?

You can find the difference in detail in below link. http://expertsharepoint.blogspot.com/2017/07/difference-between-permission-levels-of.html

If a user has “Read” permission level to a document, they can always find the document using search or browser and open it in the browser or their Office client app. If a user has “View”Only” permission level to a document, they can only find and open the document in the browser. In that case, Search doesn’t show the document!