The design of your documents contains a similar theme with your navigation on the left side with your logo at the top and your content on the right.
Changing your document logo
Click Settings on the sidebar of the Better Proposals.
You’ll be able to choose the brand you wish to edit under ‘Branding’ section and find the settings there.
Click 'Browse for logo' and replace the current one with your own. It's best to use a transparent PNG with a minimum width of 400px.