SQL & PL/SQL

Hi, i need to do this: 1) encode some pdf file with base64 algorithm 2) put the resulting - ascii ? - file into some XML tag and finally 3) decode this data back to obtain the original pdf file.

I tried to use utl_encode's package procedures base64_encode/decode but in vain (maybe due to my scarse experience). The problem is (i believe) in the last step because i start from a 70 KB pdf file and after encoding it becomes 100 KB (ok this is foreseeable) but when decoding i obtain a 50 KB file... (sort of truncation occured, because Acrobat Reader can read it for a while, then raise un error).

Is there a known issue for this problem? Someone can help or suggest?
Thank you, best regards
Massimo