Read first or shrink right away?
You don’t have to read a guide before you get started. If your PDF simply needs to get smaller, open Compress PDF and choose a method there. If the recipient specifies a maximum size, enter it in KB, MB or MiB under Reduce PDF to a target size. The tool then tries to create a file that does not exceed this value. It cannot guarantee this for every PDF.
A guide is worthwhile if the result doesn’t fit or you want to clear up a question beforehand. That’s the case, for example, if the file stays large, text becomes blurry, your device offers its own methods, or you don’t know which limit applies in the first place.
File size and image quality
How much a PDF shrinks and how it looks afterwards depends on what it consists of. For troubleshooting, what matters first is therefore what you are observing right now.
For questions about image quality, two guides complement each other. The guide to compression and quality explains what is changed in an existing PDF. The scanning guide starts earlier, with the settings of your scanner or scanning app.
Guides for your device
Every operating system offers its own ways to shrink a PDF. These ways don’t work the same everywhere. The device guides therefore name the specific app and, where it matters, the system version the steps are based on.
- Mac: with the Preview app, you export a separate copy and then check whether it has really become smaller and is still easy to read.
- Windows: you work either in the browser without installing anything or with an installed program such as PDF24 Creator, which according to its manufacturer works offline.
- iPhone and iPad: the steps are based on Apple’s user guides and each name the iOS or iPadOS version they apply to. iPhone and iPad are described separately because a process on one device does not automatically apply to the other.
- Android: the guide takes you from processing in the browser to the saved file, which you’ll find in Chrome’s downloads or in your device’s file app. Apps and menus may differ depending on the manufacturer.
- Without upload or fully offline: here you’ll learn what processing in the browser on your device means and why it still needs internet to load. It also covers installed programs that work without a network.
If the menus on your device look significantly different from those described, first compare your system version with the version named in the guide.
Job applications, email and upload portals
How large your file may be is always decided by the party receiving it. That can be an employer or its application portal, your email provider, a university or a public authority. Check there first which limit applies. Also check whether it counts per file or for all files together, and which formats are allowed.
- Prepare application documents: shrink your CV and certificates without losing pages, stamps or small digits.
- Prepare a PDF for email: find out whether your provider limits the attachments or the entire message.
- Documents for uni-assist: prepare documents for upload in My assist without losing required pages, translations or certifications.
- Receipts for ELSTER: prepare attachments for specific ELSTER forms. Each requirement applies to the form named in each case.
With Check upload limits, you compare your files with values you enter yourself from the recipient’s requirements. These include size per file, total size, number of files and pages. For this, the calculator reads the file size and, where possible, the page count of your PDFs. It doesn’t change any file and isn’t connected to any portal. A passed comparison therefore doesn’t mean that the recipient will accept the file.
Pay attention to the unit: 1 MB is 1,000,000 bytes, 1 MiB is 1,048,576 bytes. If the recipient only writes “MB”, it isn’t always clear which calculation they mean. Convert KB and MB shows you how big the difference is.
Signatures, forms and data processing
Some PDFs need not only to look good after shrinking but also to keep working. A digital signature lets you verify who signed and whether the document was changed afterwards. If a program rewrites the file, this signature can therefore become invalid. An inserted image of your signature, by contrast, is just an image. Our compressor rejects digitally signed and encrypted PDFs. PDFs with signatures and forms explains what this means for you and how forms are handled.
File processing and security describes where your file contents go during processing and what happens when you download or reset. How PDF processing works shows the process from selecting to saving.
Go straight to the right tool
Not every problem is solved by compressing. Often a different step with your PDF helps:
- Split PDF if the recipient accepts several smaller files and all pages should be kept.
- Merge PDF if a portal requires exactly one file.
- Convert images to PDF if your scans are still JPG or PNG files.
- PDF calculators for units, print dimensions, compression ratio, email size and upload time.
- All PDF tools at a glance, sorted by task.
You’ll find which files the tools accept and where their limits are under File limits and supported features.