It is necessary to follow the document structure to ensure that users can navigate through content in a logical order that is consistent with the meaning of content.
Therefore, the first outline level should always be 1. If not, the PDF will have incorrect tags and the structure will not make sense for users who are unable to see the document.
If multiple styles in the document are using outline level 1, the user will be presented with a list in alphabetical order, and be able to select the appropriate style to lead the document from this list.
The first paragraph of the document has outline level 2. This will mess up the tags and structure for a screen reader.