The best way to embed any files or documents into your proposals is to upload it to any online file storage software such as Google Drive or Dropbox.
Then once you have done that, get the direct link for that file and copy it. You can of course simply paste that link into your proposal but we're all about design and making things look awesome here at Better Proposals, so we're going to link some text to the link you've just copied.
Let's say your file is a PDF on a recent report you've published. Go into the text editor and type "Click here to download our PDF report" for example.
Then highlight it and you'll see the toolbar popup and click the link icon on the right at the end.
Then you'll see the link window appear and you can paste your link in the "URL" field and check any other settings and click "Save"
That's it! Your all good to go and your recipients can view/download your file from one click inside your proposal.