The Shifting Borders
When you create a new document in Google Docs, it loads with standard, default margins (typically one inch on all sides). If you frequently write academic papers or formal letters that require specific, non-standard margins (like 1.5 inches on the left for binding), having to manually change the Page Setup every single time you open a blank document is tedious. Furthermore, if you paste text from another heavily formatted document, Docs can sometimes incorrectly assume you want to adopt the pasted margins, shifting your carefully aligned text unexpectedly.
Locking in Your Preferred Setup
To ensure every new document starts exactly how you want it and stop Google Docs from automatically reverting to the standard one-inch margins, you must explicitly save your preferred Page Setup as the new global default.
Open a blank Google Doc. First, set up the document exactly as you want it permanently. Navigate to the top menu bar, click File, and select Page setup. In the dialogue box, type in your desired margin sizes (Top, Bottom, Left, Right). Before you click OK to apply them to this document, look at the bottom left corner of the dialogue box. You will see a button labelled Set as default. Click this button. Google Docs will silently save these exact dimensions. Now, click OK. Every single new document you create from this point forward will automatically generate with your custom margins locked in place.