Hi, I have a CD with a 'learn German' book. It contains some interactive extras as html files.
The CD seems to be divided into 2 partitions: Audio disc and Schritte plus 2

Neither Ubuntu nor Fedora can read the part with the interactive html files. I got them by copying them onto my stick from a windows laptop.

I get this:
Unable to mount Schritte plus 2
Error mounting /dev/sr0 at /run/media/pedro/Schritte plus 2: Command-line `mount -t "udf" -o "uhelper=udisks2,nodev,nosuid,uid=1000,gid=1000,iocharset=utf8,umask=0077" "/dev/sr0" "/run/media/pedro/Schritte plus 2"' exited with non-zero exit status 32: mount: /dev/sr0 is write-protected, mounting read-only
mount: wrong fs type, bad option, bad superblock on /dev/sr0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so

Anyone know why Linux can't read them??

put the cd in and post what k3b says about it.

Also

ls -A of the cd contents will be useful.

The usb copy may be defective due to crude tricks in the cd

Don't have k3b installed at the moment.
As the rest of the cd is audio, there is nothing in /media . Apparently audio cds do not have a file system, and can't be mounted, don't ask me why or how, I don't understand that! I can inspect the audio contents of the cd using the file manager, there are 33 .wav files, but no html files to be found!

The stuff I copied off of the cd to the usb stick using Windows works fine.

In that case it may be due to proprietary java scripts.
source of html files?

What happens is, Ubuntu tries to mount Schritte plus 2, I can see it in the file manager window, but it runs into a problem, see the error message above, and leaves it unmounted but visible. The html files come from the publishing house and are nothing special, an index.html and two others, and two subdirectories.

I do get some weird effects using Linux on this Toshiba laptop. This must just be another quirk!

Just to mention it:
The weirdest problem is: if I unplug the dsl cable, Ubuntu freezes. Not only that, but it cannot reboot, it freezes on the login. The only way to get Ubuntu to reboot is to start Windows, then reboot. I have reported this as a bug and asked any and all people if they know what is wrong, but nobody knows!

I believe you have a super audio cd SACD. Some of them were very odd and required downloaded apps (some by rootkit).

It doesn't sound like a SACD to me -- just a "normal" audio CD with a badly-defined partition containing files that happens to work with Windows, possibly just because it complains less.