An Caighdeán Oifigiúil (The Official Standard) is the official document that governs the grammar and spelling of the Irish language. It is often referred to as An Caighdeán (The Standard). It is published by An Gúm.
A PDF version has been made publicly available by the Translation Section of the Houses of the Oireachtas. Here is the link.
Any standard PDF reader, such as Sumatra Reader, can be used to read and search the document.