Guide
Start with what the recipient asked for
Almost every file problem starts at the other end: a portal that accepts only PDF up to 4 MB, an employer that wants one document rather than six photos, a print shop that asks for 300 DPI. Find those instructions first, because they decide the format, the resolution and how many files you send. PDF vs JPG vs PNG explains what each format is good at, with file sizes we measured, and ends with a table that matches common jobs, from a signed contract to a poster, to the format that suits them.
Then decide where the conversion happens. Are online PDF converters safe? walks through what uploading a document to a converter involves, who holds it and for how long, and the one-minute check that shows whether a site sends your file anywhere. The PDF tools, Merge PDF, Split PDF, Compress PDF, Rotate PDF, JPG to PDF and PDF to JPG, all do the work inside your browser, so a bank statement or a passport scan never leaves your device.
Articles
Where to start in files & pdfs
Start with How to Reduce PDF File Size Without Ruining It: What Makes PDFs Big and What Each Method Actually Does, How to Send a Large PDF: Email and Messaging Limits (Gmail, Outlook, iCloud, WhatsApp) and Every Way Through, and PDF vs JPG vs PNG: Which Format for Scans, Photos, Forms and Printing — they cover the most common questions in this category and each links to the calculator that matches.
4 articles are published in this category so far. Each one follows the same structure: the formula or method, a worked example, a comparison table where relevant, and a direct link to the live calculator.
Context
What to have in front of you
Have the files you actually mean to send, not copies that have already been through a messaging app. WhatsApp, Messenger and many email clients shrink photos to save data, so a picture forwarded to yourself may already have lost the detail you need. Take copies straight from the camera roll, the scanner folder or the original download.
Know the limits. Note the accepted file types, the maximum size per file and in total, whether pages must be combined, and any naming rule, such as your surname and the document type. Government and immigration portals often publish these on a help page rather than on the upload form itself, so look for it before you start rather than after an upload is rejected. How to send a large PDF lists the attachment limits of the main email and messaging services, and how to reduce PDF file size explains what makes a file big and which fix suits it.
Finally, know where the result will end up. A file that will only be read on screen can be small; one that will be printed, archived or read by text recognition software needs more resolution. Deciding that first saves converting the same pages twice.
Scenarios
Five everyday file jobs and how to handle them
A signed form on paper: photograph or scan each page flat and in good light, combine the pages into one PDF in reading order on A4 or Letter, and check every page is upright before sending. If the recipient needs to see the signature clearly, keep the original quality rather than shrinking the file.
Receipts for an expense claim: one photo per receipt, combined into one PDF with the file name printed under each image so the person checking can match receipts to claim lines. Remove the photos’ location data, which reveals where you were when you took them.
A bank statement or payslip for a landlord or lender: these are usually already PDFs. Send the original file rather than a photo of the screen, and if a portal insists on images, convert only the pages it asks for at 150 to 200 DPI. Keep the conversion on your own device; a statement carries your account details, address and spending.
A contract someone sent as a PDF, needed as images for a presentation: render the pages at 150 DPI as PNG, which keeps the text sharp. For a brochure, extract the embedded photos instead of rendering pages, so you get the pictures at the resolution they were supplied.
Identity documents for an application: follow the portal’s size limits exactly, make sure all four corners of the document are visible, and never send them through a converter you have not checked. A passport or driving licence scan is exactly what identity thieves look for.
Comparison
Container, lossy image or lossless image
A PDF is a container: it holds pages of a fixed size, and each page can hold real text, vector drawings and images. That is why it is the standard for documents. JPG is a lossy image format that throws away detail you are unlikely to notice to keep photos small, and PNG is a lossless image format that keeps every pixel, which suits screenshots, diagrams and text. A PDF can carry a JPG inside it unchanged, which is why a photo can go into a PDF without losing anything.
Converting between them has costs worth knowing. Turning a text PDF into images freezes the text, so it can no longer be searched or copied. Saving a JPG as a JPG again loses a little more quality each time. Shrinking an image to fit an upload limit is often necessary, but it is the one step that can make a document unreadable, so do it last and check the result.
Limits
What these guides and tools do not do
The guides explain formats, resolutions and privacy in general terms. They cannot tell you what a particular court, embassy, university or employer will accept, and those rules change without notice; when their instructions differ from anything written here, follow theirs.
The file tools convert between images and PDF. They do not recognise text, straighten photos taken at an angle, remove shadows, fill in forms, add passwords or verify signatures, and they cannot open a protected PDF without its password. Where a job needs one of those, the guides say which kind of tool does it, including the options built into Windows, macOS, iPhone and Android.