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%.