The following have been specifically mentioned as being able to be automated.

• PDFCreator Free, open source.  More info on using it in VBA code, including combining multiple spreadsheets into one file can be found at Printing Worksheets To A PDF File (Using Early Binding)  Also see the Late Binding page at this website.  I haven't tried converting the code to work in Access.
  Note: There is another product called PDF Creator which costs $$$.

• Adobe Acrobat
      Systemically OutPut Access Report To PDF (Both PDF Writer and Distiller are mentioned)
      Interesting problem when Acrobat/PDFDistiller is referenced with early binding
      Multiple auto file name generation w/ PDFWriter? 
       Print to a PDF File 
      Create PDF from MS Access Report  
• pdfFactory by FinePrint.
      "you can use VBA to set registry values to provide filenames/locations and print 'silently' without user intervention. "
• Pdf995 Developers FAQ
     VBA code that successfully converts an Access report to a PDF file.
     "pdf995 stores output file name and folder info in an .ini file. All you need to do is edit the .ini file in code."
     Programatically printing Access reports from pdf995 using VBA
• Win2PDF
     "automate the generation of PDFs from both Access and Excel, including assigning the file name, using Registry entries."
• ACG Soft E-mail and PDF class library for Access.  Also supports other options besides Acrobat such as Win2PDF and pdfFactory
• CutePDF Writer (Free)

I don't know which of the following can be automated.  That is you the programmer would like to programmatically control the output directory and file name.

• Freeware method  (dated given the above but still may be of interest)
     - Install Postscript printer
     - Ghostscript
     - Ghostview (Note: printing postscript files from Ghostview may require manually deleting *.tmp files located in c:\winnt\system32\spool)
     - redmon (Printer to file redirection software)
     - change the default printer just while printing to the PDF
      Systemically OutPut Access Report To PDF
      VBpdf.zip (despite the name this is a link to a web page.)   (2005-04-27)
• Free PDF (Too much advertising for my tastes but this utility does the work of the above freeware method.

• Jaws PDF Creator (I'm not sure just how well this product works with Access)
• PDF-XChange
     PDF Automation
• BCL easyPDF
• VPrinter by MaBase.De
• Access2PDF
• Access Web: Save a report's output as a PDF file  This technique requires Adobe Acrobat to be installed.
• PrimoPDF Free 

Notes

• Text in Text Fields Is Cut Off in PDF File Created from Microsoft Access at Adobe's website has some steps which may be helpful in configuring PDFs
• Adobe Acrobat Developer Center
• To simply (all things are relative) change the default printer for the duration of the report download a sample Access 97 project for changing your default printer at runtime. If you're printing, and want to change the output device simply, this code is for you. You will need to click here and find DefaultPRT.ZIP on that web page.
• VBA code to extract PDF stream from BMP (long)