When sharing files with another user via email, it’s common to use the recent documents list in the “Attach File” quick action at the top of the Compose window. This does not always work. The easiest way to share a file (especially from OneDrive) is to click on Browse this PC
at the bottom of the “Attach File” list. From there you find the file you wish to share and double-click to attach it to your email.
If you have multiple files or documents to share, it might be easier to create a shared folder in OneDrive. Click HERE to view an article on how to do this.