Acrobat Professional 8.1

When I try to run Acrobat Professional Trial on a Vista Business X86 system it reports a fatal incompatibility with Adobe Reader!!! I have uninstalled Adobe Reader and tried to remove any scraps of files or registry entries connected with it but the incompatibility continues. Instructions on how to manually remove Adobe Reader file and registry entries pop up but do not work in Vista because System files and registry entries are inaccessible even to administrators. Curiously Acrobat Professional 7 works perfectly on another Vista computer. Adobe Support will not support trial versions but I am not going to pay for an update until I know it will work! It seems ludicrous that Adobe cannot fix incompatibilities between their products. Perhaps the pdf format should be withdrawn in favour of docx? Has anybody found a solution?