The Pixelmator Pro Photos extension lets you edit your images and create graphic designs using all the tools available in Pixelmator Pro right in the Photos app. You can use it in combination with the editing tools built into Photos.
After you've downloaded Pixelmator Pro, there's nothing special you need to do to install the extension — it shows up in Photos automatically and you can start editing photos right away.
Then, in the toolbar at the top of the screen, click Extensions > Pixelmator Pro.
Note: If Pixelmator Pro isn’t available under Extensions, click Manage, then click Photos Editing in the left sidebar, and turn on Pixelmator Pro.
Save your changes by clicking Save Changes in the top-right corner or click Cancel to discard them.
When saving changes made using the Pixelmator Pro extension for the first time, you can choose whether or not you’d like to preserve your nondestructive edits — such as layers, adjustments, and effects — in your Photos library.
Preserve Edits. This will preserve any layers, adjustments, effects, and other nondestructive changes you make using the Pixelmator Pro extension and they will be restored the next time you open images edited using the extension.
Save Flattened. Only the final, edited images will be saved to your library — layers, adjustments, effects, and other nondestructive changes will be discarded.
You can change the method of saving changes at any point in the Pixelmator Pro extension preferences.
Note: To make saving edits in Photos possible, Pixelmator Pro creates a PXD file in the Pixelmator Pro folder in iCloud or the Pictures folder on your Mac. If iCloud is turned off, the documents will be automatically saved to Pictures.
You can take any existing Pixelmator Pro document and bring it over to your Photos library — all layers and nondestructive adjustments included.