Let us be honest: You want a Mort Cinder PDF because you want to read the story today without paying $300. That is a fair desire.
However, here is the wisdom from long-time collectors: Do not read Mort Cinder on a screen.
This is a book designed for reflection. You need to hold the page to see Breccia’s cross-hatching. You need to turn the physical leaf to feel the weight of the narrative. Reading a low-res scan on a phone destroys the pacing.
If you absolutely cannot find a physical copy, look for the CBR (Comic Book Reader) format over PDF, as CBR often preserves two-page spreads better. But treat the PDF only as a "preview" to decide if you want to hunt down the real book. Spoiler: You will want the real book.
If you search for "Mort Cinder PDF," you are not alone. There is a simple market reason for this: the physical book is incredibly rare.
Because the book is not currently streaming on services like ComiXology (Amazon) or available for a cheap digital purchase, fans have turned to illegitimate scanning projects to read the story.
Mort Cinder is still under copyright. In the US, the Fantagraphics translation is copyrighted. In Argentina, the estate of Oesterheld (who was "disappeared" by the military junta in 1977) and Breccia’s family still hold rights. Downloading a full PDF from a file-sharing site is technically piracy.