I get a little nerdy about editions, so here's how I break it down for myself.
When people say 'different editions' of Frederick Douglass PDFs, they usually mean two overlapping things: (1) differences in the actual text Douglass wrote and revised over time, and (2) editorial and digital differences introduced by publishers or scanners. On the first point, Douglass rewrote and expanded his life story across three major autobiographies — the original 'Narrative of the Life of Frederick Douglass, an American Slave' (the tight, fiery 1845 account), the more reflective and expanded 'My Bondage and My Freedom' (1855), and the long, later 'Life and Times of Frederick Douglass' (first 1881, revised later). Those are different works, not just reprints: chapters are added, rhetorical emphases shift, and he sometimes softens or elaborates names and events.
On the editorial/digital side, PDFs vary wildly. A Project Gutenberg or Internet Archive PDF might be an image-scan of an 1845 printing (great for seeing original punctuation and page layout) or an OCRed text with occasional errors; a Penguin, Norton, or Library of America PDF will include modernized punctuation, scholarly introductions, footnotes, and explanatory annotations. Some PDFs include illustrations or facsimile plates, others add essays, bibliographies, or teaching notes. Practically, that means page numbers, chapter breaks, and wording may not line up across PDFs — so I always check which edition my citation refers to.
If I’m studying Douglass closely I prefer a scholarly edition with textual notes so I can see why editors made changes, but if I just want the voice and immediacy I’ll grab a good scanned first edition PDF and savor the original line breaks and typography — it feels alive to me.