How to convert a PDF from letter to A4 size?

[eabase]

The examples for page size does not include an example for how to convert an already existing document to use another page size. The examples only show how to create a new page, which is not what I want.

[stefan6419846]

There is nothing like a default conversion for page sizes as this might depend on your use case. The easiest approaches are to use page.scale_to or just update the corresponding page boxes (see the docs at https://pypdf.readthedocs.io/en/stable/modules/PageObject.html) to the desired size.