Before you sign a PDF, you can save a copy of the PDF. Also, while signing the PDF, you’re prompted to save as the PDF. You can choose a different name so that you have the original PDF unsigned.
If you’re expecting others to sign the PDF, don’t select the Lock document after signing option in the Sign As dialog box or the Sign Document dialog box as described in the help page: https://helpx.adobe.com/acrobat/kb/edit-signed-PDF.html#Howtohandlesuchissuesbetterinfuture
Regards
Amal