The Universal Clipboard feature in macOS High Sierra/Mojave and iOS 11/12 allows you to copy content, including text, images, photos and video from one Apple device and paste it in another. That includes copying entire files between Macs.
To do this, make sure that: 1) your Macs support Universal Clipboard (which they should, by default); 2) both are signed into iCloud; 3) both have Bluetooth enabled; and 4) both are are on the same WiFi network. Then:
Choose the file you want to copy and paste on one Mac.
Hit Command-C on the file to copy it.
Go to your other Mac.
Hit Command-V to paste the file.
(This how-to is based on my experiences and info on Apple’s support pages — where the images sometimes come from.)