how to overcome this?i am able to read some of my pdf using below code, but still some are unreadable?

clear java
javaaddpath('C:\Users\Hp-Pc\Documents\MATLAB\PDFBox-0.7.3\lib\PDFBox-0.7.3.jar')
pdfdoc = org.pdfbox.pdmodel.PDDocument;
reader = org.pdfbox.util.PDFTextStripper;
 pdfdoc = pdfdoc.load('C:\Users\Hp-Pc\Documents\MATLAB\chemical.pdf');
pdfdoc.isEncrypted
 %%text, with planty of padding
pdfstr = reader.getText(pdfdoc)                  %#ok
class(pdfstr)
pdfstr = char(pdfstr)                            %#ok
class(pdfstr)
 %%text 'unpadded'
pdfstr = deblank(pdfstr) %#ok
%%will get an error here..
 pdfdoc = pdfdoc.load('C:\Users\Hp-Pc\Documents\MATLAB\chemical.pdf');
pdfdoc.isEncrypted
pdfstr = reader.getText(pdfdoc)                  %#ok
%%but press forward..
pdfdoc.getDocument().close;