Note: The following solution was tested for Windows 7. It should also work for Windows XP.
To covert a Microsoft Word document to a PDF document while retaining a custom page size, go to your Start Menu and click on Devices and Printers.
Double-click on the printer “Adobe PDF.”
Go to Printer, then Properties.
A window will pop up with lots of tabs. You should be on the General tab. There, you’ll see a box with the header “Paper Available.” It’ll usually say “Letter” inside. Below the box, you’ll see a button called “Preferences.” Click on that.
You’ll see a list of options pop up, and the fourth one will say “Adobe PDF Page Size.” Click “Add.”
In the box that pops up, you’ll see options for width and height. Tell it what size you want. Be sure to give name your setting before you hit “Add/Modify” (I recommend you call your new setting by the size you’re imputing: e.g. “5 x 8”). Click “Add/Modify” when you’re done.
Now, where it says “Letter” next to Adobe PDF Page Size, click on it. A list of options will pop up. Depending on what you named your page size, you might have to scroll a bit to find it. Click on the setting you just created, then hit Apply.
You’re now ready to convert! Go to the location of your Microsoft Word file, right click on the file name, and click “Convert to Adobe PDF.”
Don’t forget to change the Adobe PDF printer setting back to Letter when you’re done.