How can I keep a reference window visible while working in another app?

First decide whether you need the reference to float over the app you are typing in, or whether seeing both windows side by side is enough. Those are different behaviors: pinning keeps one window above others, while arranging windows side by side gives each a place on the screen. The available option depends on your operating system and sometimes on the app. If you know whether you use Windows or a Mac, and whether the reference is a document, webpage, or video, you can choose a more specific route.

One option is Microsoft PowerToys’ Always On Top utility. It can pin the active window above other windows; the documented default shortcut is Windows key+Ctrl+T, and the shortcut can be customized. Use the shortcut again to unpin the window, or close it. If the title-bar context-menu option is enabled in the utility’s settings, that menu can also switch pinning on or off. [S1]

A practical sequence is: open the document and writing app, make the document active, use the shortcut, then click into the writing app. Before typing, check that the document is the window you meant to pin. The shortcut applies to the active window, so selecting the wrong one can pin the wrong app.

This is a PowerToys feature, not a built-in Windows always-on-top control. Microsoft also notes that a pinned window is not guaranteed to appear above other windows that are themselves topmost, and lists possible issues involving Citrix, Remote Desktop, and VMware windows. [S1] If the shortcut does not suit your setup, check the utility’s settings rather than assuming the default is unchanged.

Yes. Use Snap to arrange the reference and your work app side by side. Microsoft documents dragging a window to a screen edge or using Windows key plus an arrow key to arrange it, then using Snap Assist to place another window beside it. [S2]

For example, put your writing app on one side and the reference document on the other. This keeps both visible, but it does not pin the reference above other windows; another window can cover it. [S2] If you need more room, Alt+Tab and Task View can switch among open windows, while multiple desktops can separate workspaces. Those are ways to organize or switch between work, not ways to keep a reference floating over another app. [S2]

Try the side-by-side layout first if your screen has enough room. If it feels cramped, switching windows may be simpler than trying to keep both visible.

For a web video playing in Safari on Mac, Apple documents Picture in Picture: start the video, open the Page menu in the Smart Search field, and choose Enter Picture in Picture. The video becomes a movable floating window that can be positioned in a screen corner and stays in place when switching desktop spaces. [S3]

To undo that, choose Restore to return the video to its original window and continue playback, or choose Close Picture in Picture to return it and pause. [S3] This applies to Safari web videos, not arbitrary reference windows or every app, and the exact interface may vary with the macOS version. [S3] If your reference is a document or another kind of window, check whether that app has an appropriate option, or use an arrangement or window-switching approach available on your system. Don’t assume video Picture in Picture will work for other windows.