Split PDF by Size: Step-by-Step
A size limit usually applies to each file or to all attachments together. Check which rule your recipient uses before splitting. Our measured eight-page example shows why two small PDF parts can still make one large ZIP.
Step 1: Check the receiving limit
Check the portal or email service’s current limit and whether it covers one file or all attachments. Leave room below that limit; a preset name does not guarantee acceptance by every provider.
MB and MiB are different units: 20 MB is 20,000,000 bytes; 20 MiB is 20,971,520 bytes. Use the units and byte limit required by the receiving service.
Step 2: Upload and split
Upload the PDF and select Split by size. Set a target below the receiving limit. PDFThin groups whole pages into parts and keeps their original order.
If a single page cannot fit, splitting alone cannot solve it. Try compression first or use a higher permitted limit. Keep the original and check the output.
Step 3: Download and check the parts
Download the result, open every PDF part and check its size and page range. Do not use the ZIP’s size as a substitute for checking each PDF.
Measured on 13 October 2026: our own eight-page synthetic PDF was 38,034,907 bytes (38.03 MB). An offline library demonstration produced part 1 with pages 1–4 at 19,016,540 bytes and part 2 with pages 5–8 at 19,016,547 bytes: about 19.02 MB each. The example used a 20 MiB target with a 262,144-byte safety margin, giving an effective per-part limit of 20,709,376 bytes. It used pdfcpu 0.11.1 through PDFThin’s lossless library path; it was not an HTTP upload or delivery test.
Step 4: Send the parts in order
Name or describe the parts in sequence and tell the recipient the page ranges. If the limit covers all attachments, send separate messages or use a transfer method the recipient accepts.
The number of parts depends on page sizes and the chosen target. A PDF around 38 MB will not always split into exactly two parts.
FAQ
Does splitting preserve page order?
Yes. Parts retain the original sequence. Check the page ranges and open every part before sending.
Will the ZIP also fit the per-part limit?
Not necessarily. In the measured example, the two parts totalled 38,033,087 bytes. A separately created ZIP_STORED demonstration archive was 38,033,305 bytes, much larger than 20 MB. That archive was not the website’s production download.
Can I split a scanned PDF?
You can try, but a single large page may exceed the target. Keep the original and check readability, images and searchable text; this example does not prove preservation for every scan.
Useful reminders
How this example was checked
The source was generated for this example, with seed 20261013, a different 2160 × 2200 grayscale noise image on each page, and native text labels and charts. It contains no customer or third-party input.
qpdf 11.9.0 checked the PDFs; Poppler 24.02.0 extracted labels and rendered all pages at 800 px. Page order and those grayscale renders matched. This does not prove preservation for other documents or guarantee acceptance by a receiving service.
Tools and more help
Use Split PDF by size for the task. The complete splitting guide explains limits and difficult cases; try compression if one page is too large.
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