Retaining Custom Page Sizes in Files Converted to PDF.When you convert a file with a custom page size, Adobe Acrobat may not retain the custom page size. To ensure that a custom page size is retained, follow the steps below:

In Windows XP:

  1. Choose "Start" -> "Settings" -> "Printers and Faxes"
  2. In the Printers dialog box, select the ""Acrobat Distiller" printer.
  3. From the menu bar, choose "File" -> "Server Properties".
    The image illustrate howto Retain Custom Page Sizes in Files Converted to PDF
  4. Click "Create a New Form". In the Form Name text box, enter a name for the custom page size.
  5. Enter the desired values in the Width and Height text boxes.
  6. Click "Save Form" and then "OK"
    The image illustrate howto Retain Custom Page Sizes in Files Converted to PDF
  7. In the source application, choose "File" -> "Print" and select the "Acrobat Distiller".

Reference: Retaining Custom Page Sizes in Files Converted to PDF Using Create Adobe PDF Online