You can't if you are using the export to Word option. Even though the .rtf option supports some graphic elements such as lines, Access does not export them. I actually wrote .rtf files from COBOL 30 years ago. The .rtf is a tagged format so you just need to get the tags in the correct spots. You could manually write the report data as a .txt file and rename it later to .rtf if Access objects to treating .rtf as a text file. In order to get the lines in, you would need to have an existing .rtf file with those objects in them. Open the .rtf file using notepad and find the code that builds the line. You then just insert the tag code where you need it when you are writing to the file manually.
If you have a pretty print problem, you are better off using Excel to produce the report. Use TransferSpreadsheet to export the data. You can export to a template that has formatting defined or you can open the spreadsheet after it is created and do some pretty printing using VBA and OLE automation.
And finally, exporting to .pdf has two advantages.
1. it prevents tampering
2. all the graphic elements are transferred.
Let us know how you want to proceed.