Downloading the file means getting the file content from the Repository, which has it stored on disk.
API Explorer URL: http://localhost:8080/api-explorer/#!/nodes/getNodeContent
See also: Download Multiple Files
When you know how to upload content to the Repository it is natural to want to download content from the Repository. The following HTTP GET call is used to download a file: http://localhost:8080/alfresco/api/-default-/public/alfresco/versions/1/nodes/{id}/content
Here we are getting the content for a file with the Node Identifier specified as the {id} URL part.
The following example gets content for a text file with the d8f561cc-e208-4c63-a316-1ea3d3a4e10e Node Identifier:
$ curl -X GET -H 'Accept: text/plain' -H 'Authorization: Basic VElDS0VUXzA4ZWI3ZTJlMmMxNzk2NGNhNTFmMGYzMzE4NmNjMmZjOWQ1NmQ1OTM=' http://localhost:8080/alfresco/api/-default-/public/alfresco/versions/1/nodes/d8f561cc-e208-4c63-a316-1ea3d3a4e10e/content Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua...
You can also just make this call (i.e. http://localhost:8080/alfresco/api/-default-/public/alfresco/versions/1/nodes/c4980e44-92ac-41a5-91dc-2b2183c61de8/content) in a Web Browser and the file will be downloaded. If you want to preview the file in the Web Browser you would need to add an extra query parameter called attachment and set it to false (i.e. http://localhost:8080/alfresco/api/-default-/public/alfresco/versions/1/nodes/c4980e44-92ac-41a5-91dc-2b2183c61de8/content?attachment=false).