How do I un-void a document?

You cannot "un-void" an envelope. You could copy the envelope which creates a new envelope with all the attributes of the copied envelope including document, Recipients, email text, and document fields.

How can I get a version of the document with all the signatures before the system watermarked it as void?

The envelope I initially sent on the 21st of January was voided just recently. I wasn't able to keep track and missed the date it was to lapse.

Is there a way to un-void it?

Only one signatory was able to sign and upload a couple of documents. I need to download those documents without the "VOID" label.