The data you entered with codepage 37 will not be correct and will have to be reentered - the characters you need from 1026 are not available in 37 and will not even really be in the database except as the "substitution" character. I'm surprised you didn't have this info, I recall it being pretty easy to find in the documentation.
You need to call JDE and ask for all information on Tier 3 language configuration, and then mention Turkish. There are some other requirements after you get the database right to be able to see the data in PDF files correctly.
Upload all the arial.ttf , ariali.ttf, arialbd.ttf, arialbi.ttf, times.ttf, timesbd.ttf, timesi.ttf, timesbi.ttf, cour.ttf, courbd.ttf, couri.ttf, courbi.ttf from your PC to the server's resource/truetype directory. Yes, the AS/400 will actually use the truetype fonts! If you use FTP, make sure you do this in binary mode. Delete (or move) the "fonts" directory from the resource directory, because the Type 1 fonts there do not have the glyphs to be able to render Turkish Characters, and JDE will use these instead of the TTFs if they are still there. Additionally, I've had to delete the fonts directory on my client workstation's Acrobat install in the Program Files directory. Then it should work. I believe this is ALL in a document on "Tier 3 language configuration" but I don't have it handy. I'm sure it is on the KG somewhere, or available via phone call. That is how I got the info a bit over a year ago when I was actually working on a Czech install (ccsid 870 for me).
You will know if the data in the PDF is right even if the fonts are wrong if you open the PDF in wordpad and view the data parts and they are correct. If this happens, then only the font stuff above is needed to be done. If the data are still wrong in wordpad, your database may still have problems.