By default, users in SharePoint can created, modify and delete file. This deletion capability also extends to files that they may not have created. This is the default nature of collaboration.
However, there are times when businesses may want an environment that allows collaboration but prevents user deletion of a file from say, a document library.
In this video:
https://www.youtube.com/watch?v=_qbWVGwdNV4
I’ll show you how to set that up. In essence, an administrator needs to create a new custom permission level in SharePoint that excludes the delete capability. They then need to assign that new permissions to the location and users where they wish to apply this. The great thing is that once it is set up, it can be used across the whole site collection.
CIAOPS 