My problem turned out to be due to my fault.
I'm very sorry, mtas.
After I tried Adam's script, I checked my installed ipdf's size.
It was about 74kb. (The copied ipdf should be 80.9kb.)
Because I think my iLiad's disk may be full,
I tried deleting the Chinese font file(mshei.ttf) and ran Adam's script.
Now all OK. I can read pdf files
My iLiad's temporary free disk space is:
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/tffsa1 73045 71190 1855 97% /
/dev/tffsa5 28065 2 28063 0% /mnt/protected
/dev/tffsa6 131180 110244 20936 84% /mnt/free
/dev/tffsa7 581 46 535 8% /mnt/settings
/dev/hda1 2026104 137364 1888740 7% /media/cf
And the deleted mshei.ttf is 1858kb. Is iLiad's free disk space such severe?
Or isn't my iLiad normal?
(Recently I installed some Japanese fonts to CF.
I may take some mistakes during it.)