Absolutely, yes. You can specify a document as locked at any point in time (document create, document edit, etc).
You can do this through the UI or through the SOAP API. Simply check relevant boxes available in the LOCK DOCUMENT section on the Document details page.
By default, edit and download locks are disabled for a document. To lock and unlock your document, you must have the Document Edit permission in addition to the Document Create permission. To prevent others from editing or downloading a document, you can choose the edit lock or the download lock as required. Selecting the edit lock automatically enables the Document Administrator to edit the document and allows you to select the download lock option.
To edit or download a locked document, the user must have the Document Edit permission. The user who has locked the document can edit or download it at any point in time. A Document Administrator that has the option, Allow Document Admin to edit enabled in the LOCK DOCUMENT section or a Site Admin can also edit or download a locked document.