I can reproduce this by setting post & upload to 128M as you have, my memory limit is also set at 128M.
Increasing this to 512M & restarting apache sees the pdf upload fine
php.ini
PHP:
; Maximum amount of memory a script may consume (128MB)
; http://php.net/memory-limit
memory_limit = 512M
According to php.net memory_limit should be larger than post_max_size. 256M should even do it.