How to send PDF document as response in a webservice?

Heelo all,i am rather new to using webservices, so please bear with me.
I could do some simple services, using SQLRPGLE, and the installation wizard from iNavigator.Usually, i define parameters (fields, structures, arrays) to be passed as JSON.
Next, i want to return a PDF document.
For my proof of concept, i am thinking of:
1. Get PDF from IFS, convert with BASE64_ENCODE into a CLOB.       (Works)
2. Convert CLOB back with BASE64_DECODE and write it to IFS for verification.    exec sql SET :myVarchX  = QSYS2.BASE64_DECODE(:myVarchOut);      (on compile, i Get SQL0312, dont know why?).

3. When this works, implement as webservice and return the Base64 encoded CLOB. 
4. How to define parameters in my RPG program? As SQLTYPE(CLOB)?

Or ist here an much much easier way of doing this? (I guess there is!)

Thank you all for hints, or maybe working examples!
Best regards from Switzerland, Martin Neugebauer