What you can change in a PDF and what you cannot
A PDF is a locked format by design — it looks the same on every device and printer, which is why businesses and government agencies use it. But "locked" does not mean "frozen." You can add notes, highlight text, fill in forms, rotate pages, crop out sections, and rearrange the order. What you cannot easily do is edit the text itself or change fonts and spacing the way you would in a Word document.
The changes you make depend on what tool you use and what the PDF's creator allowed. Some PDFs are restricted — the creator set a password that prevents annotation or copying. Most PDFs you encounter are unrestricted and let you mark them up freely. Before you spend time adjusting a document, open it and try to add a comment or highlight. If the tool refuses, the PDF is restricted and you will need the password or a different approach.
The distinction matters because it shapes which tool to reach for. If you need to fill in a form or add notes, a free reader like Adobe Acrobat Reader or your browser works fine. If you need to edit text, delete pages, or combine multiple PDFs, you need a more capable tool — and your privacy comfort level determines which one.
Key Takeaways
- Most PDFs let you highlight, annotate, and fill in forms without any special software — your web browser or free Adobe Acrobat Reader can do this.
- Editing text, removing pages, or combining PDFs requires a paid editor like Adobe Acrobat Pro or a privacy-focused alternative depending on your comfort with cloud storage.
- Always save your adjusted PDF with a new filename so you keep the original unchanged.
- Some PDFs are password-protected and will not let you make any changes until you enter the correct password.
- Free online PDF editors are convenient but store your file on someone else's server — check the privacy policy before uploading sensitive documents.
Highlighting, commenting, and filling forms in free tools
If you only need to mark up a PDF — highlight passages, add sticky notes, or fill in a form — you do not need to buy anything. Adobe Acrobat Reader, which is free, handles all of this. Open the PDF, click the "Comment" or "Annotate" button in the toolbar, and choose your tool: highlight, underline, strikethrough, or add a text box. Your marks stay with the file when you save it.
Your web browser also works. Chrome, Firefox, Safari, and Edge all have built-in PDF readers that let you highlight and add notes. Open the PDF in your browser instead of downloading it, and the same tools appear. The marks you make are saved to the file itself, not to the browser, so they travel with the document when you read it or email it.
For forms specifically, look for a "Fill" or "Form" button in Acrobat Reader. Click it and the form fields become editable — you can type in your name, address, or answers without the text appearing as a comment. When you save, the filled-in information stays in the PDF. If the form does not have fillable fields, you can still add a text box comment over the blank line, though it will look less polished.
Editing text, removing pages, and combining files
Changing the actual text in a PDF — not just adding notes on top of it — requires a real editor. Adobe Acrobat Pro is the standard tool, but it costs money and stores your files in Adobe's cloud by default. If you came from the privacy guide, you know that choice matters to you.
If you want to keep files off the cloud, desktop editors work locally on your computer. PDFtk (free, open-source) and Preview (built into Mac) let you rotate pages, delete pages, and reorder them. For text editing, Foxit PhantomPDF and PDFXChange Editor are paid options that work offline. These tools cost less than Adobe and do not require a subscription, but they have smaller user communities and fewer features.
If you are comfortable uploading to a web service, free online editors like Smallpdf, ILovePDF, or PDF.io let you edit text, delete pages, merge files, and compress size without installing anything. They are fast and intuitive. The tradeoff is that your document sits on their server during processing. Most delete files after a few hours, but read their privacy policy first — some keep files longer or use them to train AI models.
To combine multiple PDFs into one, use the same tool: Acrobat Pro, a desktop editor, or an online service. Upload or open all the files, arrange them in the order you want, and export as a single PDF. This is one of the easiest PDF tasks and works the same way across all platforms.
Rotating, cropping, and resizing pages
Rotating a page is straightforward in almost any tool. In Acrobat Reader, right-click the page thumbnail on the left and choose "Rotate Clockwise" or "Rotate Counterclockwise." In Preview on Mac, select the page and use the Tools menu. Online editors have a rotate button that appears when you select a page. The rotation is permanent once you save.
Cropping — cutting away the edges of a page to remove margins or focus on a specific section — requires a slightly more capable tool. Acrobat Pro has a crop tool in the toolbar. Free online editors like Smallpdf have a crop feature too. You draw a box around the area you want to keep, and the rest is discarded. This is useful when you are scanning a document and the scanner picked up extra white space, or when you want to extract one section of a multi-page PDF.
Resizing the entire page — making it larger or smaller — is less common but possible in desktop editors and some online tools. This is different from zooming in to read it; resizing actually changes the page dimensions in the file itself. Use this when you need to fit a PDF onto a different paper size or reduce file size for email.
Removing password protection and handling restricted PDFs
If a PDF is password-protected, you will see a message when you try to open it asking for a password. If you know the password, enter it and proceed. If you do not, you cannot open the file at all.
Some PDFs are not password-protected but have restrictions set by the creator — they prevent copying, printing, or annotating. These are less strict. You can still view the file, but certain actions are blocked. To remove these restrictions, you need a tool that can strip them. Online services like Smallpdf have an "Unlock PDF" feature that removes these restrictions without needing a password. Desktop tools like PDFtk can do the same. The restriction removal works because it targets the metadata that enforces the rules, not a password.
If a PDF requires a password to open and you do not have it, there is no legitimate way around it. Password-cracking tools exist, but they are slow and unreliable, and using them on a document you do not own is illegal. If you need access, contact the person or organization that created the PDF and ask for the password.
Saving your adjusted PDF without losing the original
Always use "Save As" instead of "Save" when you make changes to a PDF. This creates a new file with a new name and leaves the original untouched. In Acrobat Reader, go to File > Save As. In your browser, right-click and choose "Save as." In online editors, the read button automatically saves a new file to your computer.
Name the new file clearly so you know which version is which. Instead of "invoice.pdf," use "invoice-marked-up.pdf" or "invoice-final.pdf." This prevents you from accidentally overwriting the original if you need to refer back to it or send it to someone else unchanged.
If you are working with a form, the same rule applies. Fill in the form, then save it with a new name. The original blank form stays intact for the next person who needs to use it.
Comparing tools by what you need to do
| What you want to do | Free option | Paid option | Online option |
|---|---|---|---|
| Highlight and add notes | Acrobat Reader, browser | Not needed | Not needed |
| Fill in a form | Acrobat Reader, browser | Not needed | Not needed |
| Edit text in the PDF | None | Acrobat Pro, Foxit PhantomPDF | Smallpdf, ILovePDF |
| Delete or reorder pages | PDFtk, Preview (Mac) | Acrobat Pro, PDFXChange Editor | Smallpdf, ILovePDF |
| Combine multiple PDFs | PDFtk, Preview (Mac) | Acrobat Pro | Smallpdf, ILovePDF |
| Crop or resize pages | None | Acrobat Pro | Smallpdf, ILovePDF |
| Remove restrictions | PDFtk | Acrobat Pro | Smallpdf |
Frequently Asked Questions
Can I edit text in a PDF without buying Adobe Acrobat Pro?
Yes. Free online editors like Smallpdf and ILovePDF let you edit text, but your file uploads to their server. If you want to keep files offline, you need a paid desktop editor like Foxit PhantomPDF or PDFXChange Editor, which cost less than Acrobat Pro and do not require a subscription.
What is the difference between highlighting in Acrobat Reader and editing text?
Highlighting adds a colored overlay on top of the text — it is a note or mark, not a change to the actual document. Editing text means changing the words themselves, which requires a full editor. Acrobat Reader can only highlight and annotate, not edit.
If I upload a PDF to an online editor, how long does it stay on their server?
Most online editors delete files within a few hours of processing, but this varies. Check the privacy policy of the specific tool you use. Some services keep files longer or use them for other purposes. If you are working with sensitive documents, a desktop editor or Acrobat Pro is safer.
Can I remove a password from a PDF I forgot the password to?
No, not legitimately. If the PDF requires a password to open, you need the correct password to access it. Contact the person or organization that created the file and ask them to provide it or send you an unlocked copy.
Does rotating a page in a PDF change the file size?
No. Rotating a page only changes metadata — the instruction for how to display it — not the actual content. The file size stays the same. Deleting pages or compressing images will reduce file size, but rotation will not.