some pdf files that i have do not open and this message comes up

"Error --- the document cannot be opened because it is not a valid PDF file"

did anyone else get the same problem? If so, anyone figure out a way to fix it?

the source of the pdf file is the same as the other ones in a package. The other ones obviously opened without any problems. The ones that aren't opening are definitely PDF files...

the apps I tried:

adobe reader
PDF viewer
perfect viewer

Have you tried those PDF's on your desktop to see if they load fine? Are they password protected or DRM'd using ADEPT? Adobe's own reader doesn't do those, for some reason.

I tried a .pdf on my Vox. The pdf worked fine on my PC. On the Vox just the cover page showed up and the rest of the pages were pink lines. Go figure?

Maybe the file was corrupted or damaged during the transfer. You could try deleting the one on the Vox and copying it from your computer again.