I am new to ID and have designed an A3 landscaped page that I would know like to split into 2 x A4 facing pages portrait
Create a new A4 sized document with 2 pages. You can use facing pages and set the start page to an even number, or turn off shuffling from the Pages Panel flyout menu and drag two non-facing pages together or force a normally ordered facing pages doc into spreads with an odd page on the left. The object is to get two A4 pages together.
In the original file select all and copy, then in the new file paste in place.
Peter thank you for the response. You're effort has saved me. Really take my hat off to people like yourself that answer questions in these forums.