This is a really good question. Are you generating the PDF files (save as PDF) from within FileMaker? Are you using the "append" option? I need to think on this one.
Ideally I want to run a script that just creates three pdf files and "appends" them all into one file without anyone knowing.
Second best solution would be to just have the script generate three pdf files and I can merge them together manually later.
It's possible to set up an unstored calculation field such as:
gPageOffset + Get ( PageNumber )
$$PageOffset + Get ( PageNumber )
You then use a script that:
Enters preview mode
Goes to the last page and then sets the global variable or field to Get ( PageNumber )
Depending on whether you set a field or a variable you may need to drop out of preview mode, set the value and return so a variable sounds like a simpler option.
You would, of course, put the calculation field on your layout to show the page number.
Thanks for the response Phil. Sorry to be a pain here but can you (or someone else) explain your answer a little more. Although that was a clear explanation, I'm still getting a little lost (ok, a lot lost). I know how to use calculation fields and I know how to run scripts. I think it is the specifics of the scripts and using a variable that is getting me lost
Me not understanding this makes me think of this scene from back when The Office was funny. http://vimeo.com/27060669
I'll answer in terms of the first two layouts and leave it to you to extend this to three.
Define your unstored calculation field, cPageNumber like this: $$PageOffset + Get ( PageNumber ). Define it in the table that's the basis for layout #2.
Put that field on your second layout where you want to show the page number
Now use this script to set $$PageOffset to the correct number:
#On Layout #1. perform a find, sort records or whatever you need to set up the first part of your PDF
Enter Preview Mode  --> clear the pause check box
Go to Record/Request/Page [Last]
Set Variable [$$PageOffset ; value: Get ( PageNumber ) // get the page number of the last page from layout #1's part of the report ]
Save As PDF ---> generate the new PDF with the first pages of your report
Go to Layout [Layout #2]
#Do whatever you need to produce the needed found set for the second part of your report.
Save As PDF, but with the append option to append it to the PDF produced from Layout #1.