Conga Composer can render Salesforce fields that contain HTML markup using the HTML prefix. This is particularly useful for long text fields that contain the HTML line break tag (<br />) and for Salesforce rich text fields. You can also use these prefix formula fields that build HTML strings.

Syntax{{HTML:FieldName}}
ValuesFieldName is the name of the field from the Template Builder window.
Notes

Images stored directly in rich text fields are not supported and do not display in the output file.

However, if you retrieve the Salesforce download URL and add that to your rich text field, the Composer can format the image in the generated document. Your URL might look something like this: https://c.na88.content.force.com/sfc...sion/download/0681Y000004rEToQAM?asPdf=false&operationContext=CHATTER.