Yes, your documents are safe. The Discover view in OneDrive for Business never changes any permissions.
Only you can see your private documents. Also, other people can't see your private activities, such as what documents you've read, what emails you've sent and received, or what Skype for Business conversations you've been in. Other people can see that you've modified a document, but only if they have access to the same document.
What you see in the Discover view is different from what other people see. You can see your private documents and other documents that you have access to. Other people can see their documents and documents that they have access to.
Who can see my documents?
You're always in control. Only you can see your private documents, unless you decide to share them. In the Files view, you can use the icons in the Sharing column to quickly see which of your documents are shared.
Your private documents are marked with a padlock and the text Only you. Shared documents are marked with a people icon and these are the documents that show up in the Discover view.
To see who a document is shared with, from the Files view, select the people icon next to the document and look in the Details pane. Under Has Access, you can click Manage access to see more information, share the document, or stop sharing if you don't want people to discover the document.
For more information about sharing, see Video: Share documents in Office 365.
How can I share documents with others?
To make the Discover view a great experience for everyone in your network, it's important that you and your colleagues store and share your documents where the Discover view can get to them: in OneDrive for Business or in SharePoint sites in Office 365.
How can I keep a document private?
If you want to keep a document private, store it in OneDrive for Business and choose not to share it. These documents will not show up in the Discover view for other users.
In the Files view, use the icons in the Sharing column to quickly see which of your documents are shared. Your private documents are marked with a padlock and the text Only you.
If you want, you can always share a document with others later.
Can other people see what documents I’ve viewed?
No, no one can see which documents you’ve opened and viewed in the Discover view.
If you’ve made changes to a document, other people can see that you modified the document, but only if they have access to the same document.