You must set the policy of ImageMagick to allow PDF read. See https://stackoverflow.com/questions/52703123/override-default-imagemagick-policy-xml
ImagickException: unable to write blob '/tmp/magick-_1qgBrSJUIx19-Qo-u_kGKJ7LjFOtSaL': Disk quota exceeded @ error/blob.c/BlobToFile/406 in /home/masterclassonlin/public_html/e/mod/securepdf/view.php:98
Stack trace:
#0 /home/masterclassonlin/public_html/e/mod/securepdf/view.php(98): Imagick->readImageBlob()
#1 {main}