A practical way to shrink a scanned or photo-based PDF to a few hundred kilobytes for email, WhatsApp and upload forms, without making the text unreadable.
You finish a form, attach your documents and the website answers: “File too large.” Or the email bounces because the attachments together are over the limit. This guide explains why scanned PDFs get so big and shows a simple method to bring them down to a size that sends easily, using only tools that run in your browser.
A PDF made from typed text stores letters as small shapes and is usually only tens of kilobytes. A scan or a photo is different: every page is a grid of coloured dots. A modern phone takes pictures of 12 megapixels or more, which is far more detail than a page on a screen or an ordinary printout needs. When those pictures go into a PDF unchanged, the file is huge for no visible benefit.
So making the file smaller is mostly a matter of two things: saving each page at a sensible resolution, and using JPEG compression at a sensible level. Cropping away empty table or floor around the paper also helps, because there are fewer pixels to store.
This is the best case, because you only compress once.
Those per-page numbers are estimates. Pages with a lot of fine detail, shadows or colour come out larger than a clean black-on-white page, so always look at the real file size before you send it.
If someone gave you a heavy scanned PDF and the original photos are gone, you can rebuild it in two short steps.
This works well for scans of paper documents, ID card copies, receipts and certificates. It is a poor choice for a PDF that is mostly selectable text with a few pictures, because the new file will be made of images and the text will no longer be selectable. If that matters, keep the original too.
Work backwards from the limit. If a portal accepts 500 KB per file and each page is roughly 100 KB in Small mode, a document of three or four pages should fit. If the limit is 200 KB, you will probably need to keep the file to one or two pages, or to send the pages as separate uploads if the form allows it. For email, the common trap is the total of all attachments, not one file. Many mail services cap a message at around 25 MB in total, and the limit applies to the message after encoding, so leave some room.
Messaging apps have their own rules, and those rules change over time, so check the app if you are sending something very large. For ordinary documents, a PDF under a few megabytes is accepted everywhere and opens quickly on a slow connection.
Look at the file size in your phone’s file manager or in the file properties on a computer. Open the PDF and scroll through every page to be sure none is upside down or cut off. If a form rejects the file for another reason, such as the wrong format, check whether it wants a PDF or a JPG; you can switch between them with JPG to PDF and PDF to JPG.
Identity cards, certificates and bank letters are exactly the files you do not want to hand to a stranger’s server. Both tools used here run in your browser, so the pictures are processed on your own device. If you send copies of an ID, consider adding a note about the purpose of the copy; the guide on text watermarks shows how.
Almost always because it contains full-size photos. A phone camera picture is often 3 to 8 MB, so a PDF made from ten of them can pass 40 MB. A PDF made of plain text is usually tiny by comparison.
Yes, a little, and that is the whole idea. The pictures are saved at a lower resolution and with more compression. For ordinary printed pages this is hard to notice on screen, but check the result before you send it.
Not with the picture-based method in this guide. The pages become images, so the text is no longer selectable. If you need searchable text, run the file through PDF to Text with OCR and keep that text alongside the PDF.
It varies a lot. Many job and admission portals ask for anything from a few hundred kilobytes to a few megabytes per file, so read the instruction on the form and aim comfortably below it.