Sometimes you might want to read from a PDF while you’re working. Perhaps you want to consult a manual, for example.
You can make use of the Stickies app to display a PDF in an “always on top” (i.e. floating) window. Unlike using Preview to display a PDF, a Stickies note has no toolbar or other window furniture, making for a very efficient display of the PDF taking up as little desktop space as possible.
Start by opening Stickies (it’s in the Applications list of Finder), creating a new sticky note via the File menu, and making it a floating window by selecting the option on the Note menu.
Then locate your PDF using Finder and drag and drop it onto the new note. Resize the Sticky so that the PDF page is contained neatly.
And that’s all that’s needed! You can also make the window translucent using the option on the Note menu if that helps with your workflow — see the screenshot below for an example.
This stickification trick also works with movie files, which are displayed in a video frame, but no other file as far as I can see.
Once you’re done, just delete the sticky note. Remember that sticky notes don’t need saving. When you quit the app, all notes are automatically saved ready for when you start Stickies the next time.