How to merge images into one PDF: order and page size.

The short answer

Use the image-to-PDF tool: drop JPG, PNG or WebP files in, one image per page, drag the list to reorder, pick a page size, export. Pick A4 if it will be printed, "fit to image" if the recipient reads it on a screen, and leave orientation on "auto" unless your set mixes portrait and landscape. Two traps to head off: name the files 001, 002, 003 beforehand (the order then sorts itself), and remember PNG-heavy sets do not shrink much when merged — compress the images first when size matters.

When merging beats sending separate images

Three cases improve immediately. Submission: registrations, expense claims, tender documents — platforms usually accept a single PDF, and merging saves the recipient from doing it (and many people do not know how). Offline archive: scanned paper in a single file survives better than nine loose photos in a camera roll. Sending: one attachment to chat or email beats nine taps. If your actual goal is a long image to read in chat, that is a different job — use <a href="image-merge.html">image merge</a> and skip the PDF entirely.

Page size: A4 or fit-to-image

The key choice, with no better or worse — only different uses. <strong>A4 / Letter</strong>: every image sits on a uniform sheet with white margins, leaving room to stamp or annotate — choose this for printing. <strong>Fit to image</strong>: each page takes the proportions of the image it holds, so the screen view matches the original with no extra white space — choose this for on-screen reading, especially for tall screenshots. Keep orientation on "auto" so each page follows its own image; set it manually only for mixed sets. Margins are headroom for trimming and stamping, so set them to zero for screen reading.

Order: name first, drag second

The tool lets you drag pages up and down, but dragging twenty items is a chore. Name the files up front — 001-cover, 002-id-back, 003-licence — and the order falls into place by itself with no dragging. Naming also tells the recipient what each page is, which matters when pages arrive out of order in review. After merging, flip through once to confirm nothing is missing or duplicated before exporting.

Why the merged file can be bigger

A PDF simply carries the images inside it, so the container adds almost nothing. Nine phone photos at 3–4 MB each merge into roughly 30 MB — sometimes slightly more, because of conversion metadata. To slim it down, compress first and merge second: bring each image to a sensible size (around 2000 px on the long edge, keeping small print readable), then merge. Merging first and compressing afterwards takes the PDF-resampling route, which flattens text into pictures — a detour for image-based files. And if the recipient enforces a size cap (commonly 10 or 20 MB), compressing to a target size before merging is the shortest path.

Four checks before sending

One, order: flip through by page number. Two, sharpness: zoom to 100% and read the small print — a photo that looks crisp on a phone can turn soft once shrunk onto A4, and text documents are the worst case. Three, orientation: a portrait table photo can end up lying on the page; rotate that page if needed. Four, size and format: if it exceeds the cap, compress as above, and confirm the extension really is .pdf. Also remember image-based PDF pages carry no selectable or searchable text — if the recipient needs editable text, run OCR over the scans first.

想马上动手：用 图片转 PDF 合成多页文档，想拼长图看 图片合并，文件太大先用 图片压缩 压到目标大小，图片顺序乱用 文本排序 思路先理清单再传。Try it now: build the document with image to PDF, stitch a long image with image merge, shrink oversized shots via image compression, and keep the order straight before you upload.

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