You have filled in the form, prepared your evidence, and are ready to submit, only to find the portal is rejecting your PDF because it is too large. This happens constantly across government, NHS, university, and lettings systems. The good news is that it is almost always fixable. Here is a systematic approach that works for every portal, regardless of the specific limit.
Common portals and their file size limits
Different systems impose different limits, and they are not always clearly signposted:
- HMRC Self Assessment, 10 MB per document for most online submissions. Some older areas of the system have lower limits.
- NHS referral portals, varies by trust and system, but commonly 5-10 MB. Some older systems cap at 2 MB per document.
- Local council planning portals, typically 5 MB per document, sometimes lower. Planning applications with multiple drawings and surveys can hit this limit quickly.
- University application portals (UCAS, institutional portals), often 2-5 MB per document for supporting statements, transcripts, and references.
- Lettings agent portals, commonly 5 MB per document for bank statements, payslips, and ID. Some agents use generic form tools with lower limits.
- DWP and benefits portals, generally 5-10 MB, but some older pages within the system are more restrictive.
When the limit is not displayed near the upload field, assume 5 MB as your default target. This covers most cases and still leaves headroom for variation.
The systematic approach
Step 1: Confirm the exact limit
Before doing anything, look carefully for the stated limit. It is sometimes in the help text below the upload field, in the portal's FAQ, or in a guidance document linked from the form. If you cannot find it, try the portal's support contact or helpline, they will usually tell you the limit quickly.
Knowing the actual limit lets you set the right compression target rather than guessing.
Step 2: Try compress-to-target first
For most portal documents, compression alone is enough. Open PDFWhisk's compressor, upload your PDF, and select a target slightly under the portal limit. If the limit is 5 MB, target 4 MB to give yourself a margin.
After downloading, check the readability of the compressed file, particularly any small text, scanned stamps, signatures, and reference numbers. If it looks clear, you are ready to upload.
Step 3: If still too large, split then compress each part
For large documents that cannot be compressed to the limit without quality loss, splitting is the better approach. Use PDFWhisk's split tool to divide the document into logical sections, then compress each section individually. If the portal accepts multiple file uploads, you can submit each part as a separate file.
For planning portal submissions, for example, splitting architectural drawings from supporting documents into separate files often brings each under the 5 MB limit comfortably.
Portal-specific notes
HMRC Self Assessment
The 10 MB limit is generous enough that most documents compress to it easily. If you are uploading multiple years of bank statements or a large document bundle, remove unnecessary pages first, blank pages, duplicate statements, pages that aren't relevant to the specific claim or return.
Council planning portals
Planning applications often involve multiple large files, site plans, floor plans, elevation drawings, and supporting documents. Architectural drawings in particular can be large because they contain detailed vector graphics or high-resolution scanned blueprints. Splitting each drawing into its own file and compressing individually typically solves the problem. Check the portal's guidance, most planning portals specify exactly which documents to upload separately.
University and UCAS applications
For reference letters, personal statements, and transcripts, the limit is almost always achievable through compression alone. These documents are typically text-heavy and compress well. A 2 MB target is usually fine for anything that originated as a Word document or typed form.
For portfolios and visual work samples, compression is less effective. Consider submitting a representative selection of pages rather than every piece of work, then offer a full portfolio link via a cloud storage URL if the portal allows supplementary information.
NHS referral portals
Patient-facing NHS portals vary significantly by trust. If the portal is rejecting your file even after compression, it is worth calling the relevant department directly, staff can often accept documents by email or secure file transfer as an alternative to the portal upload.
A note on PDF/A format
Some portals, particularly older government and council systems, specify that they do not accept PDF/A format. PDF/A is an archival format designed for long-term preservation, and it can cause compatibility issues with older portal software.
If you are exporting from a modern document creation tool (Word, Google Docs, Canva), you are unlikely to produce a PDF/A file by default. But if your PDF originated from an archival or compliance system, it may be in PDF/A format. In that case, use PDFWhisk's compressor to re-export it as a standard PDF, the compression process typically converts PDF/A to standard PDF format automatically.
Final checklist before resubmitting
- Confirm the portal's exact file size limit.
- Remove any unnecessary pages before compressing.
- Use a target slightly under the limit (e.g. 4 MB for a 5 MB limit).
- Check readability of the compressed output at normal zoom.
- If still too large, split the document into sections and compress each part.
- Check that the portal accepts standard PDF format (not just PDF/A).
Portal upload limits are frustrating, but the fix is usually straightforward. Open the compressor, set your target, and get your document ready to submit.