Compress a PDF

Where the bytes actually live in a PDF

A PDF is a container. When a scanned marksheet weighs nine megabytes, the text is not the problem: inside the container sit full-resolution JPEG or PNG images, one per page, often captured at 600 dpi in twenty-four-bit colour. Compression therefore means re-encoding those images and rebuilding the file around them. Everything else — fonts, metadata, cross-reference tables — is rounding error by comparison. That is why a document exported from a word processor barely shrinks while a phone scan can lose ninety percent of its weight with no practical loss of readability.

Choosing a sensible target

Read the portal's exact wording before you pick a number. Banking recruitment commonly asks for each supporting document as an A4 PDF of at most 500 KB, scanned at two hundred dots per inch in true colour. Consular document uploads often use the same 500 KB ceiling and suggest A4 colour at 100 dpi, which lands around 200 to 250 KB per page. Scholarship portals frequently cap each attachment at 200 KB. Where FileKB has read the official document, the sentence and the link are on the matching page.

Greyscale is the biggest lever on scans

A page of black text photographed in colour stores three colour channels of sensor noise for no benefit. Converting to greyscale drops roughly a third of the data before any quality loss, and for a printed marksheet or certificate the result looks cleaner because the yellow cast of indoor lighting disappears. Keep colour only when it carries meaning: a photograph, a coloured seal, a signature in blue ink that a verifier may want to see as blue.

Multi-page arithmetic

A five-hundred-kilobyte cap on a six-page document is a budget of roughly eighty kilobytes per page, which is tight for anything photographed. Two habits help. First, scan only the pages the portal asked for rather than the whole booklet. Second, straighten and crop each page to the paper edge, because a photograph of a desk around a certificate spends your budget on the desk.

Scan settings that avoid the problem entirely

If you still have the original document in hand, a good capture beats any compressor. Use two hundred dots per inch, greyscale for text, JPEG rather than PNG output, and hold the phone parallel to the page in daylight. Most scanning apps have a document mode that does the flattening and edge detection for you. A page captured this way typically arrives between one and two hundred kilobytes and needs no compression at all.

When the target cannot be met

Sometimes a portal's limit is simply incompatible with a legible scan, and the honest options are to reduce page count, split the upload if the form allows several attachments, or accept greyscale at a lower dpi. Padding a PDF with filler to reach a minimum is possible but rarely required, since PDF rules are almost always ceilings rather than windows.

Check the output before you upload

Open the compressed file and read the smallest text on the busiest page. Digits are the risk: a softened eight can pass for a three in a roll number or a date of birth, and a document that a clerk misreads causes more trouble than one that was slightly too large. If any figure is ambiguous, raise the target and remove a page instead.

Local processing and why it matters more for documents

Photographs are personal; documents are sensitive. The files people bring to a PDF compressor are salary slips, bank statements, caste and income certificates, medical reports. This tool ships the PDF library with the page and does the whole rebuild inside your browser, so those documents never travel. There is no queue, no temporary storage, and no retention window to trust.