The paper size that I see in the Adobe Acrobat Reader is bigger or smaller than the value specified in the printer driver ‘Device Settings’ dialog box by 0.01 inches. For example, the size specified in the printer driver Device Settings dialog box is 9.84 x 13.93 inches; however, the size in Adobe Acrobat Reader is 9.85 x 13.93 inches.
The paper size is exactly the same as set in the printer driver’s Device Settings dialog box. Adobe calculates the paper size from the pixel value and rounds the result. The 0.01 inch difference is because of the mathematical rounding operation.
For example, the B4 paper size is defined as a 250x354 mm page. This value is 9.84 x 13.93 inches.
Adobe stores the value of the paper size in pixels using 72 DPI. Assuming that the image is generated using 300 DPI, the value of the paper width is (2953 pixel using 300 DPI) * (72 DPI) / (300 DPI, the image DPI) = 708.72, which the value is rounded up to 709. The value of 709 is stored in the PDF file.
When Adobe calculates the page size, it takes the page width value and divides it with the DPI: 709/72 = 9.8472222… This is the correct value, however, instead of showing this value, Adobe Acrobat will show 9.85 x 13.93 inches.