Twenty pages is comfortable on a phone; hundreds is not. Convert in batches.
PNG for text and tables, JPEG for photo-heavy or scanned pages.
Chat order is send order, so send them consecutively.
WeChat's built-in preview handles some PDFs and gives up on others, and older Android phones often have no app registered to open a PDF at all. The recipient sees a file name and no content, then tells you the file is broken. Images have no such problem: every chat client renders them inline.
The work happens locally in the browser, so there is nothing to install. The limit is memory: sixty pages rendered at double scale will exhaust a phone tab long before a desktop one. Convert in batches of ten to twenty pages if the document is long.
PNG is lossless and keeps small text and thin table rules crisp, at three to five times the size of JPEG. For pages that are mostly photographs or scan, high-quality JPEG is indistinguishable and much smaller. For a page of 9pt text read on a phone, PNG wins.
Images arrive in chat in send order. Export with page numbers in the filename so a recipient who saves them can reassemble the sequence, and send them in that same order without interleaving anything else.
If the destination is images anyway, the obvious move is to screenshot the pages. That drags the status bar and the viewer's toolbar into the picture, loses whatever was cropped at the page edge, and compresses an already rendered image a second time, which is exactly where small text degrades. A conversion renders the page itself, so size, margins and sharpness stay under your control, and fifty pages take one action instead of fifty.
No. Rendering happens in the browser and the PDF never leaves the device.
Choose PNG, and the highest scale the phone handles within a batch.
Yes if the filenames carry page numbers, or send one multi-page PDF instead.