Cannot edit pdf file in Acrobat 5.0

We’re receiving pdf files from a vendor that we’re opening in Acrobat 5.0. We want to copy some of the text, but cannot. The document has no security on it. We tried printing it to file with a postscript printer driver and then using Distiller, we created another pdf, but still cannot edit or select the text with Acrobat. Does it have anything to do with how the file was saved by the source? Thanks in advance for the help.