really have faced the problem myself. Even I was shocked by this mere fact but it did. I remember downloading an ebook which opened up perfectly with a pdf viewer. But then after a few months I tried open the same file again and Alas!!!
That is called DRM
it was not a bad file
BUT an INTENTIONAL killing of the file by the ?? "CR" holder
!! - GO Apollo 1201 !!! "the decade we KILLED OFF DRM "
( the 1202 was the error on Apollo 11 LEM "eagle" )
:///home /john/documents/printer specs pdf.
trying to open that location will NOT be possible
-- unless that line has many typos in it and is not correct--
see that blank space after "home" should NOT be there
also if you are using the terminal to open it you WILL NEED!!!! to use double quotes to handle those BLANK SPACES IN THE NAME
and the name of the folder is ALSO wrong
the "d" in Documents WILL BE A CAPITAL "D"
and the file name is also "off"
guessing on the REAL file name below
okular "printer specs.pdf"