I have a requirement for my document library. I want to hide or disable the download option for all users. They should only be able to view the documents.
You can set "Download to Offline clients" as No at your library level settings. Go to Library Settings --> Advanced settings --> select NO To download
Refer my answer in similar thread
If you want to disable the download-option for your users, they should have View Only permission level. Permission levels Read and any greater include the permission for downloading a file.
View Only permission levels still includes the following permissions:
View pages, items, and documents. Any document that has a server-side file handler can be viewed in the browser but not downloaded. File types that do not have a server-side file handler (cannot be opened in the browser), such as video files, .pdf files, and .png files, can still be downloaded.
Information Rights Management is the only way to protect the documents and don't allow user save the document in his/her system. You need to setup IRM on your network and the enable it in Central Administration.
You can find the step and more detail from below links