A2 size PDF ... Open in Photoshop turns into A3 ... Why ?

I pdf-ed a AutoCAD Drawing into a A2 PDF ...

I opened that PDF in Photoshop ... But it turns out changing into A3 ...

I closed it & retry but it still comes out as A3 size ...

Can anyone here knows how to solve it ?

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The File is PDF in Resolution 300 ... Open in Photoshop also using Resolution 300 ... While opening the PDF file, Dialog prompted ... Crop to: Media Box, Width=420.16, Height=594.08 ------------------------------------------------------------ ------------