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.
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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:
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Choose the file you want to copy and paste on one Mac.
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Hit Command-C on the file to copy it.
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Go to your other Mac.
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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.)