UPSC signature requirements
The UPSC form checks the file type, pixel size and file size in KB before it accepts an upload. 108pdf applies all three in one step, then shows the final size with a clear pass or fail check.
For CSE and several other exams, UPSC asks for your signature three times on one white sheet. Photograph the whole sheet, crop to it, and 108pdf keeps it inside the allowed pixel and KB ranges.
Why uploads get rejected
The most common reasons are a file above the KB limit, a file below the minimum KB, the wrong format (PNG or HEIC instead of JPG), and a face that is too small or too dark. The size and format are handled for you here; for the photo itself, use daylight and a plain wall.