OmniDocHow to Annotate a PDF: Highlight, Comment and Save
Learn how to annotate a PDF by highlighting, adding comments and saving a copy, and see which edits OmniDoc's PDF editor handles directly.
Marking up a PDF is a common task. You might need to question a contract, mark up a research paper or complete a form someone else wrote. Many people search for how to annotate a PDF because the file looks like it should accept highlights and notes, yet the tool in front of them does not show the right controls. The problem is usually a mismatch between the kind of markup you need and the tool you opened, not a broken file.
This guide gives you a general, platform-neutral procedure. It separates highlights and comments, which most PDF readers handle, from the edits that OmniDoc's PDF editor does directly. Those edits include editing paragraph text in place, signing, filling forms, redacting, page operations, OCR for scanned pages, comparing two PDFs and exporting. You will also see how to save your work so the original stays untouched.
How do you annotate a PDF? The short answer
Use a PDF reader's markup tools for highlights and comments, use OmniDoc's PDF editor for changes to text, forms, signatures and redactions, and save the result as a new copy.
| Your situation | What to do | Why |
|---|---|---|
| You want to highlight passages or leave notes for yourself or a colleague | Use the markup tools in a PDF reader, then save the commented copy | OmniDoc's PDF editor, as described in its feature list, does not include highlight or comment tools |
| A word, date or sentence needs correcting | Open the copy in the OmniDoc desktop client and edit the paragraph text in place | Paragraph text editing is a listed editor function |
| A form needs names, dates or other entries | Fill the form fields in the PDF editor | Form filling is a listed editor function |
| You must sign the document or hide private details | Sign in the PDF editor, or redact the passage before sharing | Signing and redaction are listed editor functions |
| The pages are scans with no selectable text | Run OCR in the PDF editor first, then mark up the recognized text | Scanned pages usually have no text you can select or highlight until they are recognized |
Before you start
- Check whether the PDF has real text. Try selecting one line with your cursor. If the words highlight, the page has a text layer. If nothing selects, the page is probably an image, and you will need OCR before you can mark up the words.
- Decide whether you need the original. Edits and annotations change the file you save. Keep an untouched copy so you can compare later or send the source to someone who asks for it.
- Confirm who will receive the file. A marked-up copy may contain private notes or details you plan to remove. Know the audience before you decide what to redact or delete.
- Install the OmniDoc desktop client if you plan to edit text, sign or redact. It is available for Windows, macOS and Linux at download.omnidoc.top. The web version of the editor is at app.unidoc.top, but the PDF editing features described here are part of the desktop client.
- Check whether the file is protected. Some PDFs block editing or annotation. If the file refuses changes, you may need permission from the document owner before you continue.
Marking up a PDF step by step
- Make a working copy. Duplicate the file in your folder and open only the copy for markup. If you make a mistake, the original is still intact.
- Run OCR if the pages are scanned. Open the copy in the OmniDoc desktop client and use its OCR feature. This gives the pages text you can search, select and check.
- Highlight the passages. In a PDF reader's markup tools, select the text and apply a highlight. Highlighting the text itself keeps the marked words easy to find later.
- Add comments. Attach a short note to a highlighted passage or place one on the page. Short notes are easier to scan and easier for the next reader to act on.
- Edit text where a fix is needed. In the PDF editor, change the paragraph text in place. Check each edited paragraph afterward, because you are changing the document's text, not adding a note beside it.
- Fill forms and sign. Complete the form fields, then use the signing feature in the editor to add your signature. Review the page where the signature appears before you move on.
- Redact anything that should not be shared. Use the redaction feature on the exact text or area. Do this after the other edits, so the final review covers the finished file.
- Save or export the final copy. Save it under a new name. Export to Word, Excel or PowerPoint only if the recipient needs an editable format.
Check the result
Reopen the saved copy and go through it page by page before you send it.
| Check | How to see it | If it's wrong |
|---|---|---|
| Highlights and comments are present | Open the saved copy in a PDF reader and scroll through each marked page | Re-apply the markup on the copy; the original is unchanged |
| Edited text reads correctly | Compare each changed paragraph with the original, side by side | Edit it again. For OCR text, check the recognized words against the scan, since recognition can misread characters |
| Form entries and signature are right | Reopen the file and confirm the values appear in the fields and on the correct page | Fill the fields again and re-sign if the signature landed on the wrong page |
| Redacted text is really gone | Try selecting or searching for the removed words | Redact again and save. Covering text with a box alone can leave the words in the file |
| Page count and order are correct | Scroll through the pages and compare with the original page count | Undo the page change in the editor and repeat it on a fresh copy |
OCR and text edits can introduce mistakes, so check any important figure, name, date or clause against the source before you rely on it.
❓ FAQ
1. Can you annotate a PDF for free?
Whether a tool is free depends on its own terms, so check those before you start. When you compare options, look at file size limits, whether a watermark is added to the output, where your file is processed and whether the layout survives saving.
2. Can I compare two versions of an annotated PDF?
Yes. The OmniDoc PDF editor includes a compare feature for two PDFs. Use it after a round of edits to see what changed between your working copy and the version you sent out.
3. Can I sign a PDF someone sent me?
Yes. Use the signing feature in the OmniDoc PDF editor to add your signature to the file. If you need other people to sign, OmniDoc also supports sign requests, where you send the PDF for signers to complete online.
4. Is covering text with a black box the same as redacting it?
No. A box drawn over text can hide the words on screen while the text stays in the file. Use the redaction feature to remove the content, then reopen the saved copy and try to select or search for the removed words.
📝 Summary
To annotate a PDF, highlight and comment in a PDF reader, make text, form, signature and redaction changes in OmniDoc's PDF editor, and save a new copy. Work on a duplicate, run OCR on scanned pages, and reopen the result to confirm every change before you share it.
