For anyone interested I found a solution to the issue. I had to shrink the pages of the source documents themselves before the PDF export was done. Fortunately, the customer was willing to accept a change to the source documents themselves.

Here is the C# code: 

namespace WorkflowActivity.Scripting.SDKScriptToShrinkPagestoBriefcaseArchiveFolder
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Data.SqlClient;
    using System.Text;
    using System.IO;
    using Laserfiche.RepositoryAccess;
    using Laserfiche.DocumentServices;

    /// <summary>
    /// Provides one or more methods that can be run when the workflow scripting activity is performed.
    /// </summary>
    public class Script1 : RAScriptClass102
    {
        /// <summary>
        /// This method is run when the activity is performed.
        /// </summary>
        protected override void Execute()
        {
            // RASession will get the Repository Access session

            // set vars for page size conversion
            // Page width measurements
            decimal pageWidthWanted = 8.5M;
            decimal pageXRes = 0;
            decimal pageWidth = 0;
            decimal pageInchWidth = 0;
            int pageWidthScale = 0;

            // Page height measurements
            decimal pageHeightWanted = 11.0M;
            decimal pageYRes = 0;
            decimal pageHeight = 0;
            decimal pageInchHeight = 0;
            int pageHeightScale = 0;

            // Final amount to scale page by
            int scalePageTo = 10000;

            //get the document info for the current entry. This is the entry to export
            DocumentInfo docInfo = (DocumentInfo)this.BoundEntryInfo;

            //Create a Document Exporter
            DocumentExporter docExporter = new DocumentExporter();
            docExporter.IncludeAnnotations = true;
            docExporter.AllowInterpolation = true;
            docExporter.PageFormat = DocumentPageFormat.Tiff;

            //Iterate through each page of the document.
            for (int i = 1; i <= docInfo.PageCount ; i++)
            {
                //Get pageinfo of current page 1,2,3,4,etc...
                PageInfo currentPage = docInfo.GetPageInfo(i);

                pageXRes = currentPage.ImageXResolution; //pixels per inch
                pageWidth = currentPage.ImageWidth; // in pixels
                pageInchWidth = pageWidth / pageXRes;

                pageYRes = currentPage.ImageYResolution; //pixels per inch
                pageHeight = currentPage.ImageHeight; //in pixels
                pageInchHeight = pageHeight / pageYRes;

                //Work out amount to scale image by with 10,000 being 100% and 5000 being 50% for example.
                pageWidthScale = Decimal.ToInt32(Decimal.Divide(pageWidthWanted,pageInchWidth) * 10000);
                pageHeightScale = Decimal.ToInt32(Decimal.Divide(pageHeightWanted,pageInchHeight) * 10000);

                //Use the smaller of the two numbers between width or height scale for the amount to scale the page by
                if (pageWidthScale < pageHeightScale) { scalePageTo = pageWidthScale;}
                else {scalePageTo = pageHeightScale;}



                if (scalePageTo != 10000)
                {
                    docExporter.ScaleFactor = scalePageTo;
                    docExporter.AllowInterpolation = true;

                    using (MemoryStream ms = new System.IO.MemoryStream())
                    {
                        docExporter.ExportPage(docInfo, i, ms);

                        ms.Seek(0, System.IO.SeekOrigin.Begin);

                        // Write page back to Laserfiche document
                        using (Stream writer = currentPage.WritePagePart(PagePart.Image, (int)ms.Length))
                        {
                            byte[] buffer = new byte[0x8000];
                            int count;
                            while ((count = ms.Read(buffer, 0, buffer.Length)) > 0)
                                writer.Write(buffer, 0, count);
                        }
                    }
                }
            }
        }
    }
}