macOS ships with a bunch of pre-installed applications that are incredibly useful to some users, and insignificant to others. But an app that's pre-installed on all the best Macs that nearly everyone will use is Preview. It's a jack-of-all-trades app, offering functionality as a photo viewer, document viewer, and an editor for both file types. Power users might change their settings and make a third-party app the default for opening images and documents, and casual users might just use Preview for viewing files. However, macOS users of all skill levels can make use of the Preview app's hidden features. These are five things that the Preview app can do, and you might not know about them yet.

5 Converting file types

You can convert file formats in the Preview app or in the Finder

Since Preview is known for being an image and file viewer first and foremost, the most common utility the app offers is arguably file conversion. Now, it's worth noting that using Preview to convert files isn't actually the quickest way to do that. A little-known trick (Right Click > Quick Actions > Convert Image > File Type) in the Finder app is still the fastest. However, file conversions in the Preview app are still very useful. You can take a look at the file you're going to convert in Preview before doing so, or make edits to the original file before exporting. Either way, if you want to convert an image or document in the Preview app, this is how you do it:

1. Open the image or document in the Preview app.
2. Click the File button in the Menu Bar.
3. In the export window that appears, adjust the file name and format as needed.
4. Click the current file format (i.e. JPEG, PDF) to reveal a dropdown menu.
5. Select the new file format you want to convert to from the list.
6. Click export to finish.

4 Marking up images and documents

The built-in markup tool can be used for annotations, drawings, and more

There are plenty of ways to add drawings or text to an image or document, such as via web tools or photo editing apps. Preview is arguably the fastest and simplest way to do so, though, because it is pre-installed as the default file viewer on macOS. After opening up an image or document in Preview, you're only a few clicks away from annotating your document with the markup tool. Here's how you can start using it in three easy steps:

1. Open the image or document in the Preview app.
2. Click the markup icon (it looks like a pen inside a circle) in the Preview app toolbar.
3. A new toolbar will appear, containing drawing tools and text boxes, among other features.

3 Merging PDF documents

It's a paid service in Adobe Acrobat, but free in macOS Preview

One of my favorite tools in the macOS Preview app allows users to merge documents together. Some of the biggest PDF viewers, such as Adobe Acrobat Reader, require a subscription to combine PDFs together. A lot of the free options available are clunky, or are web-based and require you to upload your documents to a third-party server. But you can merge two documents together with Preview on macOS completely free. As long as the two documents are discoverable in Finder, they can be merged in only a few minutes. Here's how to do it:

1. Open the first image or document you want to merge in the Preview app.
2. Click the Edit tab in the Menu Bar.
3. Hover your cursor over the Insert menu, and then click Page from file.
4. Finally, select the second document you want to merge from the Finder.

2 Removing image backgrounds

You don't need fancy editing software to remove a background

Another tool that people usually turn to third-party photo editors for is background removal. However, the Preview app on macOS can actually remove basic backgrounds from images. The functionality is pretty basic, and works best with high-contrast photos. For example, something like a digital render with a white background can be transitioned into a transparent PNG using the Preview app. You'll still want to use a more advanced photo editor for precise background removal and photo editing. You can try out background removals in the Preview app with the steps below:

1. Open the first image or document you want to remove the background from in the Preview app.
2. Click the Tools tab in the Menu Bar.
3. Select the Remove background option from the list.
4. Click Convert to change the file to the PNG format.
5. The background will now be removed from your image.

1 Signing documents

Create a signature once, and add it to documents forever

Perhaps the top feature in the Preview app is the one that allows you to sign documents effortlessly. In the Preview app, you can create multiple signatures and save them on your Mac. Then, when it's time to fill out and sign a form, you can insert the saved signature in your document in seconds. It's really easy to create and use signatures in the Preview app, since a trackpad, webcam, or iPhone can be used to first create a signature. After that, it takes only a few clicks to insert your signature. Here's how to create a signature for the first time, and insert it at any time:

Creating a signature for the first time

1. Open an image or document in the Preview app.
2. Click the Tools tab in the Menu Bar.
3. Hover your cursor over Annotate, then Signatures.
4. Click Manage Signatures.
5. Use either a Trackpad, Camera, or your iPhone to add and save a new signature.

Inserting saved signatures into documents

1. Open an image or document in the Preview app.
2. Click the Tools tab in the Menu Bar.
3. Hover your cursor over Annotate, then Signatures.
4. Click the saved signature you want to insert from the list.

Can you use Preview on every Mac computer?

The great thing about these Preview app tools is that they work on just about any Mac you use on a daily basis. Nearly all of these features have been present in the Preview app for years, if not longer, so you don't need a specific macOS version to use them. Chances are, you'll be able to fire up the Preview app on the Mac you're using right now and try out these killer tools for yourself. Updating to the latest macOS version, which is currently macOS Sonoma, is always a good idea if you aren't finding these Preview features easy enough.