You don't need a plugin.
In the blog go to the Media tab and upload a PDF. That will then create the link to the uploaded file. Then link that as you would any other link in a post.
This would be the workflow:
1. Media > Add New
2. Upload the file
3. Copy the File URL that is at the bottom of that box.
4. In your post create the words you want to link, say "here is the PDF you need"
5. Highlight those words with Shift+arrows on your keyboard or right-clicking.
6. When highlighted click the little icon in the toolbar that looks like a chain link
7. Enter the File URL
If you upload a bunch at once then later need a link, use the little icons above the writing area and go to the Media library to find the item and it's link.