Just to be sure: security groups on fileshare are not copied to Teams documents?

I am a rookie Teams admin (worked with SharePoint before) and I have a question: we are migrating files from the Windows fileshare to Teams. After migration we want to put the files on the fileshare at read only. I think that people who are member of the Team can drag the read only file to their Teams documentlibrary and then have the right to edit the file. Is that correct? 

Because a member of a Team site has edit rights for the document library in a general (standard) channel?