REDACTED

The secret was hidden in plain sight: the PDF concealed text visually, but the text was still there to copy.

The reveal

Open TISC-26-091-SINGULARITY.pdf, select everything with Ctrl+A, and paste it into a text editor. Among the hidden text fields is a suspicious Base64 string:

VElTQ3tCUk8hUmVkYWN0UERGc1Byb3Blcmx5TGFoISEhfQ==

Decoding it gives the flag:

TISC{BRO!RedactPDFsProperlyLah!!!}

The lesson is as short as the solve: hiding PDF text on screen does not remove it from the document.