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How to check and reduce PDF size and pages
Application portals often limit a PDF to a maximum size, such as 500 KB, and a maximum number of pages. This guide shows you how to measure your PDF and shrink it when it is too large.
A PDF feels like one file, but it has two numbers that matter: how many kilobytes it takes up, and how many pages it contains. A portal may accept a 2 MB document, or it may reject anything over 500 KB. It may allow 10 pages, or only one. You cannot tell either number just by looking at the file's name, so you have to measure the file before you upload it.
The fastest way to measure is the PDF Checker on SubmitSure. Upload the PDF — it stays in your browser — and the tool reads its real size and counts its pages. Then type in the limits from the portal, such as 500 KB and 5 pages, and the tool tells you PASS or FAIL for each limit. That takes a few seconds, and it is far better than uploading to the portal and hoping.
If your PDF is too large, the cause is almost always images inside it. A scanned document is really a set of photographs, one per page, and photographs are heavy. A single scanned page can be 1 to 2 MB. Text-based PDFs, made by exporting from Word or Google Docs, are usually much smaller, because text takes almost no space.
To shrink a scanned PDF, scan again at a lower resolution if you can — 150 to 200 DPI is usually enough for a form, while 300 DPI is only needed for fine print. If you already have the PDF, open the images inside it in an image compressor, reduce each one to a reasonable size, and rebuild the PDF. Many free PDF tools also have a compress or reduce-size option that does this in one step.
If the problem is too many pages, look for pages that do not need to be there: blank pages, a cover page the portal did not ask for, or the same document scanned twice. Remove them with any PDF editor before you upload. Merging is the opposite problem — if the portal wants one PDF and you have five separate files, merge them first, then check the size and page count of the merged file, because merging can push you over the limit.
Keep a copy of the original PDF before you compress anything. Compression is a one-way step: once detail is removed, you cannot get it back. If the portal later asks for a clearer copy, you will want the original. And always check the compressed file on screen — if the text is unreadable, the compression was too strong, and you should use a gentler setting.
Do it in 3 steps
- Measure it — Upload the PDF to the PDF Checker and read its real size and page count.
- Compare with the limits — Type the portal's limits in, and see PASS or FAIL for each one.
- Shrink it — If it is too large, compress the images inside it or remove extra pages, then check it again before uploading.
Common mistakes to avoid
- Do not just rename a file to .pdf — a renamed image is not a real PDF and the portal will reject it.
- Do not compress so hard that the text becomes unreadable — an unreadable document is worse than a large one.
- Do not forget to check the merged file, not just the separate pages — merging changes the total size.
- Do not scan in colour if the document is black-and-white text — greyscale scans are much smaller.
Frequently asked questions
How do I know how many pages my PDF has?
Upload it to the PDF Checker. It counts the pages from the file itself and shows the number next to the file size.
Why is my PDF so large?
Almost always because it contains scanned images. Re-scan at 150–200 DPI, or compress the images inside the PDF, and the size usually drops by more than half.
Can I reduce PDF size without losing quality?
A little, yes. Removing unused pages and using greyscale for text documents loses almost nothing. Heavy compression of images does lose detail, so check the result on screen before uploading.
Is my PDF uploaded to a server?
No. The PDF Checker reads your file inside your browser. It is never sent anywhere.