EPUB vs PDF: choosing an ebook format
The right format depends on the document and how you want to read it, not on the filename alone.
EPUB follows the reading area
EPUB packages publication text, images, styles and navigation. Many novels are reflowable: text can adapt to your screen and chosen type size. That is useful on phones and for extended reading. Chapters and saved content locations can remain useful even when pagination changes.
Not every EPUB behaves that way. Illustrated publications may use a fixed layout, and Japanese books may define vertical writing or ruby annotations. Respecting that design can limit typography, spread or highlight controls. EPUB 2 and EPUB 3 are supported, but unusual publisher features still require compatibility testing.
PDF keeps a designed page
PDF is useful when the original position of text, diagrams and images matters. Zoom and page-fit controls enlarge that layout rather than reflowing a novel into new lines. This preserves the document but can require more panning or scrolling on a small screen.
A PDF can contain selectable text, scanned page images or both. Search and passage notes depend on an extractable text layer and document permissions. A clear image of words is not automatically searchable text, and ReadVeranda does not add OCR.
Other extensions do not imply compatibility
MOBI, AZW3, FB2 and CBZ are not supported by the current reader. ACSM is normally an authorization or delivery file used by another reading system, not an EPUB with a different extension. DRM can also prevent an otherwise familiar format from opening. Renaming any of these files to .epub or .pdf does not convert it.
ReadVeranda provides no conversion or DRM-removal tool. Obtain a lawful, compatible edition from your provider when possible. If you use another conversion application, check the resulting layout and accessibility yourself; a changed extension alone says nothing about the quality of the output.