Some PDFs do not snap to the window while using Preview
The problem is the document.
Typically, documents are set at 100%, so no matter the size of the window, it will automatically resize to fit the window.
However, the actual page size may be set to a different value when it was created so, when opening, it starts at that value.
From Adjusting PDF Views
The actual size for a PDF page is typically 100%, but the document may have been set to another magnification level when it was created.
Since you have Acrobat Pro, try creating a new PDF document and set the page properties to be at 100%.