If your document is not the correct size, you can resize it using the Print To PDF function.
WINDOWS
Open the document that must be resized and attempt to print. When presented with your printer options, select 'Adobe PDF' or 'Microsoft Print to PDF'. Resize the pages in the PDF by using the Page Sizes & Handling controls or by selecting "Shrink Oversized Pages", as seen in the illustration below.
Click Print to rename and save the file. Use the new version of the document when you re-file the document(s).
APPLE OS / MAC
Mac users should open their PDFs in the Preview app, then click on the "Show Markup" toolbar 
and select the "Adjust Size" button 
. Input new values for width and height - specifically 8.5 inches for width and 11 inches for height.
For more information, please refer to: Resize, rotate, or flip an image in Preview on Mac
LINUX
- Open the Document in your PDF Viewer.
- Press Ctrl+P to open the print dialog box or click File, select Print in the Menu.
- On the Menu Settings page, Click the General tab, and under Printer name, choose Print to File as your listed Printer.
- Choose your filename (rename the document) and save location.
- Select your file format. PDF is the default file type.
- Select any page preferences.
- Click the Page Setup tab to select your paper size from the Paper drop-down menu under the Paper tab.
- Click Print to save the PDF.