To print a PDF in custom sizes on a PC
Choose File > Print
Click Size, and choose one of the following options:
Click Custom scale, and resizes pages by the percentage you specify.
To print a PDF in custom sizes on a Mac
Scale up A4 to A3 as you print
1. Choose File > Print.
2. Use your default printer (Black2Sided) or choose a different print type.
3. Click Printer Properties.
4. Choose the Effects tab.
5. Select Print document on:
6. Click the arrow next to A4 and choose A3.
7. Ensure Scale to fit is selected.
8. Click OK.