How to bring a PDF under a form’s size limit

First, find out why it is large

There are two kinds of PDF and they behave completely differently.

A scanned PDF is a container holding one image per page. Its size is essentially the size of those images, and it compresses the way images do.

A digital PDF — exported from a word processor or downloaded from a bank — contains text, fonts and vector graphics. Its size comes mostly from embedded fonts and any images placed in it, and re-compressing it as an image is usually the wrong move.

If it is a scan

This is the common case for marksheets and certificates, and it is the easy one.

The scan resolution is almost always far higher than it needs to be. 600 dots per inch is roughly four times the data of 300, and for a document that will be read on screen, 200 to 300 is plenty.

Converting the pages to greyscale also cuts the data substantially, and for a document that was black text on white paper there is nothing to lose.

Scanning in colour when the document is black and white is the single biggest avoidable cause of an oversized PDF.

If it is a digital PDF

Do not convert the pages to images in order to compress them. That discards the selectable text, makes the file look worse on screen, and often makes it larger rather than smaller.

The usual culprits are embedded fonts, particularly if several were used, and high-resolution images placed into the document. Re-exporting from the original source with font subsetting enabled and images downsampled is the correct fix.

If you no longer have the source, re-printing to PDF at a lower image quality setting is a reasonable fallback — but check the text is still selectable afterwards.

What you should not do

• Do not delete pages to meet a size limit unless the portal genuinely does not want them.
• Do not convert a document to JPEG just to make it smaller. Text in a JPEG looks noticeably worse, and many portals reject image uploads where they asked for a PDF.
• Do not apply repeated compression passes. Each one degrades the content further.
• Do not reduce resolution so far that a registration number or a seal becomes unreadable. Being rejected for illegibility wastes more time than the original problem.

Checking the result

Open the compressed file and zoom in on the smallest text before uploading — a registration number, a date, a signature. If you cannot read it comfortably at 100 per cent zoom, the portal reviewer will not either.

Check the page count too. Some compression tools silently drop pages, which is a serious problem on a certificate.

Finally, confirm the file is genuinely under the limit with a margin, for the same 1000-versus-1024 reason that catches photographs.

Questions people ask