If your PDF file contains different page sizes, like letter and legal, you can specify that the pages print on the correct paper size. The Choose Paper Source setting tells a printer to select the paper tray that best suits each page.
Windows
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Choose File > Print.
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From the Page Scaling pop-up menu, choose Fit to Printable Area.
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Select the Choose Paper Source by PDF Page Size option.
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Click OK to print.
 
Mac OS
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Choose File > Print.
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(Reader X/Acrobat X) Click the Printer button at the bottom of the Print dialog box, and then click Yes when prompted.
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Make sure that the Print dialog box is in the expanded mode by clicking Show Details in the Print pop-up menu.
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From the Layout menu, choose Paper Handling.
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Select the Scale to Fit Paper Size option.
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Click Print.