I have got yesterday Perl 5.005 for Acorn-machines and.... txt2pdf runs!
No problem - no change in the script is necessary. I recommend following things: Users (with RiscOS 3.5) should use X-files (or a similar filesystem) - if someone have RiscoS 4.0 there is no need for X-Files.

Create a new X-Files-drawer and unpack the perl-script and the configuration file to this new drawer.
Then they have to change the filetype of the script (txt2pdf) to PERL (the !Perl-appliaction must be seen by the filer).
Now they can use in taskwindow/shell the script.

For viewing the new pdf-document - you have to set the filetype to PDF and view the pdf-file with !PDF.

Tested with a RiscPC/StrongARM-200 and RiscOS 3.5 (64MByte RAM).

I hope this helps!