Apt-get will not work because you did not install it with apt. When you click on
a .deb file it launches Gdebi which is the graphical interface for dpkg.

Try to use gdebi or dpkg.
sudo dpkg --remove <name of package>

There is a lesson to be learned here. Always use the repositories unless you
have no alternative. Adobe reader is available in the repositories and the open
source readers such as Evince are usually faster anyway.

I would use the repositories but in 8.04 Adobe isn't there.

Thanks for correcting me on removing a .deb - makes sense when one
thinks about it. But still got the same problem. After removal if one
does a google on .pdf - one gets a screen window

"Could not launch Adobe Reader 8.1.3. Please make sure it exists in
PATH variable in the environment. If the problem persists, please
reinstall the application."

Before pdf were just downloaded and then read with Evince. So a config
file is left somewhere i imagine.

I've just used Opera and it seems that adobereader sets up something
for any browser as the same thing happened.

Not sure but i think i've solved it.

When Adobe installs it automatically sets the preferences of the browser.

Firefox--Edit--Preferences--Applications--pdf document (set todefault
viewer i.e. evince)
Seemed to do the same in Opera.

When you have got rid of it try and find a Linux version of 'Foxit'
seems to do everything with pdf's and integrates with Firefox (
Windblows version ok)

Thanks for the suggestion. I used to use Foxit on windoze but it
wasn't able to cope with some of the maths symbols and i reverted to
acrobat.

But i did look up Foxit today and noticed it has a Beta version of
Foxit v1 which one can compile - posted just two days ago 20 jan 09.
Foxit v1 had some glitches in it i seem to remember and v2 was well
sorted about 2006. As for the current repository alternative xpdf i
wasn't impressed.

The point was that adobereader upset the browser and efax-gtk. Evince
is good for everyday use reading many formats [including tif for
faxes] but again can't handle maths symbols so well. Once i've sorted
out that glitch it'll be ok.