On your Dashboard, you have a list of all your sent and signed documents. All the signed documents will have a tick beside the document titles.
Find your document and click on the title. In the drop-down menu that appears you have the option to Download the document. If you click on Audit log/details in that drop-down list you can also download the final PDF on that page.
If you would like final signed PDFs emailed to you, then this is a setting that can be switched on in Admin > Signer Experience > Email Options (you must have administrator permissions).
If you do not see your signed document in your listings then it may be in the archive. Click on Signed documents archive in the Docs section. If the document has been in the archive for a while then the PDF document may have gone into deep storage and requires a few hours for retrieval. If this is the case then when you click to download your document you will get a small pop up message to tell you the document is being retrieved. When it is available for download you will be emailed (this may take up to a few hours later).