Portals check six things: file size, page count, encryption, MIME type, structural validity, and page dimensions. If you rule out each in order, one of them explains the rejection. When in doubt, run the file through a repair pass and strip anything the portal might not like.
Upload portals are unforgiving because they have to be. They ingest millions of files a day from strangers, so any hint of trouble means an automatic reject. The error message stays vague on purpose. Detailed rejection reasons help attackers probe for weaknesses. That leaves you guessing, which is why the same six problems account for almost every upload failure.
Cause 1: the file is too big
By far the most common. Portals publish a size limit in the upload widget, and files over that limit are refused immediately. The limit varies by portal, but common numbers cluster in a predictable range.
- Indian government portals (UPSC, SSC, tax)100-500KB
- US immigration (USCIS, State Dept)Under 5MB per file
- UK Home Office and Companies HouseUnder 5MB per file
- Corporate ATS (Workday, Greenhouse)1-2MB for resumes
- US federal e-filing (PACER)5MB per document
- Insurance and banking KYCUnder 5MB per file
- SharePoint document libraries2GB technical, 100MB practical
The fix is compression, targeted at the portal's stated size. Our size-specific compressors iterate quality until the file fits: 100KB, 200KB, 500KB, 1MB, 2MB, 5MB.
Cause 2: too many pages
Less common but very real. Some portals enforce a maximum page count independent of file size. Legal e-filing systems commonly cap at 50 or 100 pages per upload. Academic portals often cap manuscript uploads. Government forms almost universally cap ID uploads at one or two pages.
Fix by splitting the file. Use Split PDF to break the source into portal-sized chunks and upload as separate submissions.
Cause 3: the file is encrypted
Many portals reject password-protected PDFs even if the user provides the password. The portal system needs to inspect the content for indexing, virus scanning, or search, and encrypted files block all of that. The upload succeeds visually, then the server-side scan fails and the file is bounced from the queue.
Cause 4: the bytes do not match the extension
Portals often verify that the file's actual bytes match a real PDF signature. Files renamed from other formats (a Word document saved with a .pdf extension, an image with a swapped name) fail this check even though they look correct in a file browser.
%PDF at position 0. Open the file in a plain-text editor. If the first four characters are anything else, it is not a PDF. Re-export from the original source, or open it in a real PDF viewer and save as PDF from there.Cause 5: the PDF structure is slightly broken
PDFs are databases of interconnected objects. Slight corruption, from an interrupted save or an out-of-spec exporter, can leave the file readable in your reader but unacceptable to a strict validator. Portal validators tend to be strict.
Repair rebuilds the file structure from whatever objects survived. Even if you cannot open the "broken" version, a repair pass often produces a clean copy that uploads without complaint. Try Repair PDF before assuming the file is genuinely bad.
Cause 6: the page dimensions are wrong
Rare but real. Some portals enforce specific paper sizes (A4 or Letter) and reject anything else. Custom or non-standard pages, common in scanner outputs or in design work, hit this restriction.
Fix by normalizing to a standard size. Open the file in a reader, print to PDF with paper size explicitly set to A4 or Letter and scaling to "Fit to page". The output has uniform dimensions and clears the portal check.
The five-minute diagnostic
Run through the checks in this order. Most rejections resolve at step 1 or 2.
Check the size
File Manager or Finder shows the byte count. If it is over the portal's cap, compress first.
Check page count
Open the PDF, look at the page counter. If over the cap, split.
Check for password
If the file opened without prompting for a password but the portal still refuses it, run through Unlock PDF anyway to strip owner-password restrictions.
Check the header bytes
Text editor, first four characters. If anything other than %PDF, re-export from source.
Run repair
If nothing above applies, repair-and-resave produces a clean structural copy.
Normalize page size
If still rejected and the portal has a paper-size hint, print to PDF at that specific size.
The "boring PDF" recipe
For truly strict portals (government submissions, court e-filing, medical uploads), start with the source and build a maximally portable PDF from scratch.
1. Remove encryption. Any password, any restriction, gone.
2. Flatten forms and annotations. Flatten PDF bakes interactive layers into the page.
3. Strip metadata. Remove Metadata clears author, creator, and title fields.
4. Compress under the stated cap. Match the portal's size limit exactly.
5. Repair as a final rebuild. Run through Repair PDF for one last clean save.
Compress a PDF to the portal's exact limit
Auto-target 100KB, 200KB, 500KB, 1MB or 5MB. Iterative quality tuning inside the browser.
Common questions
Details that come up before hitting Submit again.
01Why does the portal reject my PDF without saying why?
Portals rarely explain rejections in detail because a detailed error would help attackers probe the system. Six causes account for most rejections: size, page count, encryption, damaged structure, wrong MIME type, and page dimensions. Ruling them out one at a time is faster than trying random fixes.
02What is a MIME type problem?
Some portals verify that the file's bytes match its .pdf extension. If the file was renamed from another format, or the extension was set by hand, the byte-level check fails. Fix by re-exporting from the original or by opening the file in a real PDF viewer and saving as PDF from there.
03Do government portals ban encrypted PDFs?
Yes. Many government and financial portals reject password-protected PDFs because their indexing and archival systems cannot inspect the content. Remove the password with an unlock tool before uploading.
04What is the safest way to prepare a PDF for a strict portal?
Compress under the stated size, remove any encryption, flatten form fields and annotations, strip metadata, and re-save through a repair pass. The result is a maximally portable, boring PDF that almost any portal will accept.
05Can page dimensions really cause a rejection?
Occasionally. Some portals enforce specific paper sizes such as A4 or Letter. Custom or non-standard pages, common in scanner outputs, can be refused. Fix by printing to PDF with an explicit paper size and fit-to-page scaling.
06Does PDFslime upload files during any of this?
No. Every tool runs entirely in your browser using WebAssembly. Files are read into local memory and never sent to a server. That matters especially for the sensitive documents portals usually require.