How to compress a PDF for an online form or upload portal

Job boards, university admissions systems, visa and immigration services, insurance claim forms, rental applications and government websites all set their own upload rules. The figures differ from one site to the next, sometimes from one form to the next on the same site, and they change over time. That is why this guide gives no numbers: check the limit on the portal's upload page at the moment you apply.

The limit is usually printed next to the upload button or in the instructions for that step. Look for wording such as "maximum file size", "files must be under" or "accepted formats". If nothing is shown, the help pages or FAQ of that particular service are the next place to look.

Read the small print twice. Some portals have one limit per file and a second one for the whole application, and some accept only PDF even when the browse dialog lets you pick a photo.

A PDF exported from a word processor stores letters as text, which takes up very little space. Weight comes from pictures: a phone photo of a passport page, a degree certificate scanned at the highest resolution, or a dozen receipts photographed one after another.

Modern cameras capture far more detail than anyone needs to read a document on screen. Compression removes that surplus by re-encoding images at a lower quality or resolution, while real text and vector graphics are left exactly as they were.

The steps below use Compress PDF. It works inside your browser tab, so the document goes straight from your device to the portal and is never handed to a third server on the way.

1. Open Compress PDF and drop your file onto the page, or choose it from a folder.
2. Pick Target size, then select one of the suggested sizes or type your own under Custom.
3. Set the target a little below the limit you read on the portal, because some upload systems count file size slightly differently.
4. Press Compress. You will see the size before and after, and a clear message if the target could not be reached.
5. Open the downloaded copy and zoom in on every page. Reference numbers, stamps and signatures should be easy to read.
6. Upload the compressed copy and keep the full-quality original somewhere safe.

A file with few or no images barely shrinks, and the tool tells you how far it got rather than pretending it hit the target. Match the problem to a fix:

Plenty of forms want everything in a single file: a cover letter, proof of address and a copy of your ID, for example. Merge first, then compress. Merge PDF puts the files in the order you set, and compressing the combined file means the limit is applied once, to the thing you actually upload.

If some of your documents are photos, turn them into a PDF with JPG to PDF before merging. Each image becomes one page, and the new file can join the others like any PDF.

Rejected uploads are annoying; rejected applications are worse. A blurred date or an unreadable account number can send a form back to you days later, so spend a minute scrolling through the compressed copy from start to finish.

One more detail: if the original was password-protected, the compressed copy is not, and bookmarks and form fields are not kept either. For most portals that is exactly what you want, but avoid leaving the unprotected copy in a shared folder or a downloads directory that other people use.