Upload caps are usually 2 MB, 5 MB or 10 MB, and the culprit is almost always scanned pages or photographs. Compress to the exact number the portal asks for: the images are re-encoded, the text layer is left alone, and the document stays readable.
1Type the portal’s limit as the targetCompress PDF works down to the number you give — 2 MB, 5 MB — rather than guessing at a quality setting.
2Check the result before uploadingOpen the before-and-after divider under the result and look at the page with the smallest print. That is where over-compression shows first.
3If it will not reach the target, split itSome portals accept several files. Splitting by size fills each part to just under the limit, so you upload the fewest files.
4Re-scan if the source was wrongA 200 MB scan of a five-page form was made at the wrong settings. 300 DPI grayscale will produce a fraction of the size at the same legibility.
Why does this happen?
The pages are scans at a high DPI. Scanning at 600 DPI in color produces roughly 10 MB a page. At 200–300 DPI a document page looks the same on screen and in print.
It is built from phone photos. A 12-megapixel photo is 3–6 MB. Twenty of them make a file no portal will take.
Everything was scanned in color. A black-and-white form scanned in color costs three times what grayscale does, with no gain.
Images were inserted at full size. A screenshot dropped into a report keeps its original pixels even when displayed small on the page.
Questions
What size should a PDF be for an online form?
Follow the portal’s number. Where none is stated, under 5 MB is accepted almost everywhere, and under 2 MB is safe for older government systems.
Will compressing make the text blurry?
Not on a digital PDF: the text is vector and is left untouched. On a scan, the whole page is an image, so heavy compression does soften it — check the preview.
The portal rejects it even under the limit. Why?
Some portals also cap page count, page size or refuse encrypted files. Check for a password on the document, and for pages larger than A4.