OmniDocHow to Annotate a PDF on Mac
Learn how to highlight, comment on, and mark up a PDF on a Mac, including scanned files, and when to use OmniDoc's macOS client for signing and editing.
Marking up a PDF on a Mac is usually simple until the file is a scan, or until you need to sign or compare it too. This guide is for anyone who needs to highlight passages, leave comments or circle figures in a PDF on macOS, and it covers both digital and scanned files.
You will learn which tool to use for each kind of markup, how to prepare a scanned PDF so you can mark it up, and how to save the result without losing the original. The short version is that your Mac's built-in PDF viewer handles highlights and notes, while OmniDoc's macOS client covers signing, form filling, redaction and version comparison.
How do you annotate a PDF on a Mac? The short answer
Use your Mac's built-in PDF viewer for highlights, underlines, notes and shapes, and use the OmniDoc desktop client when you need to sign, fill, redact, run OCR or compare files.
| Your situation | What to do | Why |
|---|---|---|
| Digital PDF, you want highlights and comments | Open it in your Mac's built-in PDF viewer and use its markup tools | Digital PDFs already contain selectable text, so you can mark it up directly |
| Scanned PDF, you need to highlight text | Run OCR in the OmniDoc desktop client, then mark up the result | Scanned pages are images, so there is no text to select until OCR adds it |
| You need to sign or fill a form | Open the file in OmniDoc and use the sign or form tools | These are listed features of the OmniDoc PDF editor |
| You want to change the wording of a paragraph | Edit the paragraph text in place in OmniDoc | Editing changes the content; annotation only adds marks on top of it |
| You have a marked-up draft and an older version | Compare the two PDFs in OmniDoc | A comparison shows what changed between versions |
Before you start
Check these points before you open the file. Each one prevents a common problem later.
- Keep an untouched copy of the original. Markup changes the file you save, and a clean copy lets you start over or compare later. Duplicate the file in Finder before you open it.
- Confirm whether the PDF is digital or scanned. Try selecting a line of text. If the cursor selects words, the PDF has a text layer. If nothing selects, the pages are likely scanned images.
- Decide what the markup is for. Highlights and notes suit review comments. If someone must sign or fill a form, you need a different step, so plan for it now.
- Install the OmniDoc desktop client if you need it. Download it from download.omnidoc.top for macOS. You only need it for OCR, signing, forms, redaction or comparison.
- Know who will read the file. Markup that looks clear on your screen may look different in another viewer, so you will want to check it on another device later.
Annotating a PDF on your Mac, step by step
- Check whether the PDF has selectable text. Open the file, then drag across one line. If the words highlight, go to step 3. If they do not, go to step 2.
- Run OCR on a scanned PDF. Open the file in the OmniDoc desktop client and use its OCR feature on the scanned pages. Save the result as a new copy so the scanned original stays unchanged.
- Open the PDF in your Mac's built-in PDF viewer. Use the OCR copy from step 2 if you made one. Otherwise, open the original digital file.
- Turn on the viewer's markup tools. Look for the annotation or markup mode in the viewer's toolbar. Once it is on, you can add marks to the page.
- Highlight or underline the text you want to flag. Select the words with the cursor, then apply a highlight or underline. Marks stay attached to the text, so they move with it if you zoom in or out.
- Add notes, shapes or text boxes where needed. Use a note for a comment, a shape to circle a figure, and a text box for a short answer on the page. Keep notes brief so they stay readable when the page is printed.
- Save the marked-up file under a new name. Use a name such as "contract-review-v2" so the earlier version remains available. Your original copy from the "Before you start" section stays as it was.
- Sign, fill or compare in OmniDoc if the task requires it. Open the marked-up file in the OmniDoc desktop client to add a signature, fill form fields or redact text. To check changes against an older draft, use the compare feature on the two PDFs.
Check the result
Review the file before you send it or rely on it. These checks catch the problems that show up most often.
| Check | How to see it | If it's wrong |
|---|---|---|
| Highlights sit on the right words | Zoom in and compare each mark with the text under it | Undo the mark, zoom in further, and select the words again |
| OCR text matches the scanned page | Select a few lines and compare them with the page image | Rerun OCR from a clearer scan, and check important names and numbers by hand |
| Notes are readable on other devices | Open the saved file on another computer or phone | Shorten the notes or move longer comments into a separate document |
| Signature or form fields land on the right page | Scroll through the pages and check each placement | Move the item in OmniDoc, then save a new copy |
| The original is untouched | Compare the original copy with the marked-up file | Restore the original from your duplicate and repeat the markup |
OCR output is generated by software, so it can misread characters, especially on blurry or skewed scans. Check any figures, dates or names against the page before you rely on them.
📝 Summary
Highlights and notes go in your Mac's built-in PDF viewer, after you run OCR on any scanned pages in the OmniDoc desktop client. Use OmniDoc for signing, forms, redaction and version comparison, and keep an untouched copy of the original throughout.
❓ FAQ
1. Do I need to install anything to highlight a PDF on a Mac?
No. The PDF viewer that comes with macOS handles highlights, underlines, notes and shapes on digital PDFs. You only need the OmniDoc desktop client if the file is scanned or you need to sign, fill or compare it.
2. Does OmniDoc add highlights and comments?
The OmniDoc PDF editor covers editing paragraph text, signing, filling forms, redaction, page operations, OCR, comparison and export. Highlights and sticky-style notes are not part of that list, so use your Mac's PDF viewer for them.
3. Can I send an annotated PDF for others to sign?
Yes. OmniDoc supports sign requests, which let you send a PDF to other people to sign online. Check the file for markup you want to keep before you send it.
4. Will my comments survive if I export the PDF to Word?
OmniDoc can export PDFs to Word, Excel and PowerPoint. Markup may not carry over in the same form, so open the exported file and confirm that your highlights and notes appear before you rely on it.
