I found this solution that worked for me. Apologies for the lack of accreditation, I didn't save the URL.
*posted from another thread - dunno if you still need the info but i figured it might help someone*
had this problem awhile back - from what i understand, the pdf viewer isn't deleted when you delete the icon, it just now becomes hidden. what i did was hook up my pre (in developer mode) via usb to my pc and use webosquickinstall to send this file by clicking on the menubar, then tools, then receive file:
to my pc desktop, then edit it with notepad/ wordpad by deleting the only item that was listed:
[ com.palm.app.pdfviewer ]
then send the edited file on the pc desktop back onto the pre via webosquickinstall by going to menu, tools, send file:
then reboot your pre. the pdf viewer should now be back permanently - well assuming you install the do not remove pdf viewer patch in preware asap, lol. dunno why palm allows the option for the pdf viewer to be hidden/ "deleted" in the first place - seems a bit silly.
this is how i remember fixing it if i recall correctly. let me know if this works for you as well.