You are required to purchase every emblem piece available from the shop. There are quite a few pages worth (including fonts, symbols, numbers, etc). Each emblem piece will cost 5,000 au. Buying every piece will cost you roughly 3 to 4 Million au.
Being that the emblem pieces are exactly the same ones in Armored Core: V, I would advise you to purchase all of them in AC:V first. Importing your player data from AC:V into AC:VD, imports all emblems purchased as well. Therefore, skipping this step all together. However, you are only allowed to import your data once!
The remaining emblems are acquired by destroying enemy ACs while progressing through the story missions and sub-missions that contain ACs. If there's nothing left in the shop to purchase, then this achievement will unlock upon completing Mission 10.