Compatibility comes before assumed size savings
A format change is useful when another application cannot read the original, but it does not always make the file smaller. An efficiently encoded AVIF or HEIC may become a larger JPEG. Compare the output and then use a separate compression target if the destination also enforces a byte limit.
Some source features do not fit in a JPEG
JPEG does not preserve transparency or animation. GIF conversion takes the first frame, TIFF conversion takes the first page, and HEIC conversion produces a conventional still image. Keep source files for the pages, sequences, metadata, and specialist properties that this browser workflow does not export.
Convert a representative sample first
Before processing a mixed batch, inspect a typical file and the most difficult one. Check text, edges, transparency, and orientation in the output. This is particularly useful for scans or unusual encodings, where the extension alone does not guarantee that the browser decoder can read every variant.