After the quarterly TSG (SA, CT, RAN) Plenary Meetings, the 3GPP produces Word documents. Afterwards the ETSI publishes the PDF versions for the releases that have been frozen (i.e. from June 2018, up to Rel-15).
The ETSI does not publish the PDF version for studies (8xx numbers, and sometimes 7xx numbers).
Except for a few cases, a 3GPP document of a given release is a superset of the same document for the previous release. When this is relevant, the ToC (Table of Contents) shows the evolution of the document according to the releases.