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It belongs with our practical guides to putting documents and websites online, which begin with how to make a website without coding, and it pairs with our guide to scanning several pages into one PDF.
How the steps were prepared: they follow Apple’s iPhone User Guide for iOS 27 and Google’s Drive Help page, and the button names are theirs. Menu names can differ on your version, so use the wording as a map, not a script.
Why scans are big
A scanned PDF is not text. It is a set of page images, one per page, and each image holds everything the camera captured. Three things make the file grow.
- More pages. Every page adds another image.
- Higher image quality. More pixels per page means more data per page.
- Colour and marks. A page scanned in colour, with shadows and stains, holds more detail than one with clean black text on white.
This is why a ten-page form can be larger than a book chapter saved as text. The text was never text; it was pictures of text.
Some scanners also add a layer of recognised text so the PDF can be searched. Google’s Drive page, for example, says that when you choose .pdf the scan is saved as a searchable PDF. That helps you find words, and it does not remove the images underneath.
Check the limit first
Before you change anything, read the limit on the page you are uploading to. Do not guess it, and do not rely on memory, because forms differ.
Then do the arithmetic. A limit of 2 MB across 8 pages is about 2,000 KB divided by 8, or roughly 250 KB per page. Units vary a little between systems, so treat that as a target and leave some room. If you know the figure per page, you know how hard you need to push each setting.
| Question | Why it matters |
|---|---|
| What is the maximum file size? | It sets the target |
| How many pages must the document have? | It sets the size per page |
| Does the form need a PDF, or will a JPEG do? | Some portals accept images, and an image can be smaller |
| Does the text need to be selectable? | It affects whether you keep recognised text |
Make it smaller at the source
Work in this order, and check the size after each step.
- Scan only what is asked for. Do not scan blank backs, covers or spare pages. Fewer pages is the largest saving, and it costs no quality.
- Delete pages you do not need. On iPhone, Preview shows page thumbnails: touch and hold one and tap Delete Page. In the Drive scanner on Android, Delete removes a page before you save.
- Crop closely. Both scanners let you adjust the crop. Cutting away the table or desk around a page leaves less to store.
- Pick a plainer filter. The Drive scanner’s Filter option changes colours or makes the image grayscale. If a page is only black text, a plainer filter may help, but the page does not promise a smaller file, so check.
- Choose the format that fits. Drive lets you save as .pdf or .jpg. If the portal accepts one image per page, that may be an option.
The last two points are the ones to test rather than assume. Compare the sizes before and after, and keep the version that is both small enough and readable.
Compress on iPhone
Apple’s guide describes a compression route in Preview.
- In Preview, open the PDF.
- Tap the control next to the filename, then tap Export.
- Choose a file format. For a PDF, the options Apple lists include Optimize Images for Screen, which reduces image resolution for screen viewing and creates a smaller file, and Save Images as JPEG, which saves embedded images as JPEG for a smaller file.
- Tap through, choose a location, optionally rename the file, and tap Save.
If you export the pages as images instead, Apple notes that for HEIC and JPEG a Size slider lets you drag left for a smaller file or right for higher quality. The same export screen has Embed Text, which runs OCR so the PDF is searchable, and Create Linearized PDF, which optimises the file for fast web loading. Neither is a size setting, so leave them as they are unless you need them.
You can also rework the file before exporting. Apple’s page on moving and deleting PDF pages shows how to delete a page, rotate it, drag a thumbnail to a new position or crop a page.
Compress on Android
Here we stay within what the sources say. The Google Drive Help page on scanning describes the steps to scan: open Drive, tap the camera icon, capture the page, adjust it with Crop and Rotate, Filter, Clean, Add, Retake or Delete, tap Done, name the file, choose .pdf or .jpg, and tap Save. It does not describe a setting that sets the file size, so we do not claim one.
What you can do on Android, using only those controls, is the source-side work above: scan fewer pages, delete extras, crop closely and decide between .pdf and .jpg. If the file is still too large, do the arithmetic again and decide whether the portal needs the full document at full quality.
Privacy: what happens when you upload a document to an online tool
A web-based compressor works by receiving your file. A copy leaves your phone, and what happens next is governed by that service’s own policy: how long it keeps the file, who can open it, and whether it is deleted. You can read a policy; you cannot see what happens on the other side.
So match the method to the document.
- A public leaflet or a menu: the risk of an online tool is low.
- An identity paper, a bank statement, a contract or a medical letter: use a method that stays on your phone, or ask the recipient if they accept a larger file.
- Any site you do not know: do not upload.
If you are choosing an app for documents, read its privacy label first: our guide to reading app privacy labels before you install shows how. Apple’s Preview and Google’s Drive scanner are the two routes this guide describes, and both come from the platform makers.
How to check the result before you send it
- Size. Check the new file size where your phone shows it, for example in the file’s details or on the attachment line of your mail app. It must be under the limit with some margin.
- Readability. Zoom to the size a reader will see. Small print, stamps and signatures are the first things to blur.
- Page count and order. Scroll through every page.
- Name. Give the file a plain name, since some portals dislike unusual characters.
- The original. Keep the full-size scan. If a portal rejects the small one, you can try again.
If the document is really a page you want people to read online, a web page can replace a large PDF: see how to build a landing page in one evening.