Hi @RPAZR,
Thank you for reaching out, this is tied to a specific signing path, not a general setting.
The Lock Document After Signing option only appears with a certificate-based Digital Signature, not with a typed or drawn signature, and it needs to be set at the field or signing step; it is not automatic.
In desktop Acrobat:
If the document does not already have a Digital Signature field, add one through Prepare Form. Then double-click it to open its properties, go to the Signed tab, and choose Mark as read-only, selecting All fields, All fields except these, or Just these fields.
Otherwise, the Sign with a Digital ID dialog shown at the actual signing step includes a Lock Document After Signing checkbox directly.
This lock is permanent, including for the signer, so it should be used only as the last or sole signer. Reference: Permissions and limitations of signed PDFs
In Adobe Sign, this works differently: a Digital Signature field automatically locks the completed document once signed, with no checkbox to select. Reference: Overview of Digital Signatures in Adobe Acrobat Sign
Let us know whether this is desktop Acrobat or Adobe Sign, since that determines whether the fix is enabling a setting or if something is already working as intended.
Thanks,
Tariq