Any document you can write to takes files dropped from your desktop. What a drop does is decided per file:

RDF

A file in one of the triple syntaxes — .ttl, .nt, .rdf, .owl or .jsonld — is imported as data: its triples are added to the document's graph

File

Anything else is uploaded to the document: the bytes are stored content-addressed under uploads/ and the document describes them as a file, titled after the filename

1. Open the document that should hold the file
2. Drag the file over the page. An overlay appears, naming both outcomes: RDF imported as data, File uploaded to this document
3. Drop it. The document reloads in Read mode with the file among its resources; an image is shown inline

A file larger than the instance's upload limit is refused before it reaches the platform, and the page says so without navigating away.

Alternatively, upload through a form:

1. Click the Create expand_more dropdown at the bottom of the page
2. Click on File in the dropdown list that appears
3. Fill out the mandatory File fields in the form:

   Filename

   Select file from your filesystem

   Title

   Enter file title

4. Click Save

A file is uploaded to the document that will hold it, so create that document first. Uploading Nancy Davolio's portrait from the Northwind demo:

doc=$(ldh create item \
  --title "Nancy Davolio" \
  --container "${LDH_BASE}employees/")

ldh add file \
  --title "Nancy Davolio" \
  --file employees/nancy.jpg \
  --content-type "image/jpeg" \
  "$doc"

The command prints the content-addressed URI of the upload as its only output:

https://localhost:4443/uploads/35fd362792e8c4bc3560a6de02f25ee551d68d02

That URI is stable across instances — it is derived from the file content alone — which is what lets the Northwind CSVs reference their images by hash before they are even uploaded. --content-type is optional — the media type is detected from the file when it is not given.