The California Secretary of State instructions for the Articles of Organization form state on there that service-based businesses can't operate via LLC unless there is an affirmative clause in the California Business Professions Code authorizing the subject profession with the ability to do so. The California BPC § 6400 et seq. does not contain authorizing clause for Legal Document Assistants profession to operate via LLC. Therefore, Legal Document Assistants are limited to incorporation or sole proprietorship.
That said, some Legal Document Assistants filed as LLCs, but the LLC limited liability protections will be tested later when invocation become necessary. Would a court pierce the corporate veil? Well… do you feel luck?