OmniDocFree Ways to Annotate a PDF: Tools and Options
Compare desktop readers, online annotators and OmniDoc's PDF editor for highlights, comments, edits, signing and forms, with a general markup method.
If you want to annotate a PDF at low cost, you usually face one of two jobs: marking up a document so others can read your notes, or changing the document itself. A reviewer who needs to highlight a contract and leave a comment has different needs from someone who must fix a typo, sign a form, or remove a phone number before sharing a file. Many desktop readers and online tools handle the first job well and the second job only partly.
This guide is for people who want an option that fits a specific task. It compares three common approaches: desktop PDF readers, online PDF annotators, and the PDF editor in the OmniDoc desktop client. It also explains a general method for highlights and comments, so you can still mark up a file if the editor you choose does not offer those tools.
Which annotate pdf free option fits your file? The short answer
Use a desktop PDF reader for highlights and comments, and use an editor when you need to change the text itself, sign, or fill in fields. Check first whether the PDF is a scan, because scanned pages need OCR before most markup and editing works well.
| Your situation | What to do | Why |
|---|---|---|
| You only need highlights and sticky-note comments | Use the markup tools in a desktop PDF reader | Leaves the original text unchanged and works well for one reviewer |
| You need to correct a typo or rewrite a sentence | Open the file in OmniDoc's PDF editor and edit the paragraph text in place | Changes the text itself, not a comment placed on top of it |
| You need to sign or fill in a form | Use the PDF editor's signing and form-filling tools | Handles both tasks in one place |
| The PDF is a scan | Run OCR first, then mark up or edit the result | Scanned pages are images, so their text cannot be selected or edited reliably until recognized |
| The file must hide certain details before sharing | Use redaction in the PDF editor on the sensitive text | Removes the content rather than covering it with a shape |
How each approach works
Desktop PDF readers with markup tools
Most desktop PDF readers let you select text and apply a highlight or underline, or place a comment at a point on the page. The reader stores the markup either in the file or alongside it, depending on the program, so check how your reader saves its notes. Some readers also let you draw shapes or add text boxes.
This approach suits reviewing, studying, and giving feedback on a copy of a document. It falls short when you need to change the text itself. Editing features differ widely between readers, and some readers limit what you can do with a file, so test the reader on a sample PDF before you rely on it.
Online PDF annotators
Online annotators run in a browser. You upload a PDF, add highlights, comments or drawings, and download the marked-up version. Nothing needs to be installed, which makes them convenient for a one-time task on a computer you do not own.
The trade-offs are file size limits, watermarks or feature limits on some plans, and the need to trust a third-party site with your document. Before you upload a contract, medical record, or other confidential file, read the site's privacy terms and confirm what happens to the file after you download the result.
OmniDoc's PDF editor in the desktop client
The OmniDoc desktop client for Windows, macOS and Linux includes a PDF editor. You can download it from download.omnidoc.top. In the editor, you can edit paragraph text in place, sign the document, fill in form fields, redact content, insert, delete, rotate, reorder, merge or split pages, run OCR on scanned PDFs, compare two PDFs, and export to Word, Excel or PowerPoint.
This approach suits corrections, signing, form filling, and redaction. It falls short for pure markup: the product facts do not list highlight or sticky-note comment tools in the PDF editor. If you need those, pair the editor with a desktop reader. Editing also changes the content of the file, so save an untouched copy before you start.
📊 At a glance
| Approach | Highlights and comments | Edits existing text | Signs and fills forms | Install needed |
|---|---|---|---|---|
| Desktop PDF readers | Core use | Varies by reader | Varies by reader | Yes |
| Online PDF annotators | Core use | Varies by site | Varies by site | No |
| OmniDoc PDF editor | Not listed in the product facts | Yes, in place | Yes | Yes, desktop client |
🎯 Which approach fits you?
If you only need to highlight a document and leave notes
A desktop reader is usually the simplest path. Select the text, apply the highlight, and add a comment where needed. Save the marked-up copy under a new name so the original stays intact.
If you need to correct or rewrite text in a PDF
Open the file in the PDF editor in the OmniDoc desktop client and edit the paragraph text in place. This is the right choice when a comment would not fix the problem, such as a wrong date in a letter or a misspelled name on a form letter.
If you have to sign or fill in a form
Use the PDF editor's signing and form-filling tools in the desktop client. If the form is sent to others for signature, OmniDoc also offers sign requests, which let you send a PDF for others to sign online.
If the PDF is a scan
Run OCR before you try to highlight or edit. Scanned pages often look like text but cannot be selected. To check, try selecting a single line: if the selection stops at the image edge, the file probably has no text layer. After OCR, check the recognized text against the page, because recognition can miss or misread characters.
If the file contains details that must not be shared
Use redaction on the sensitive text in the PDF editor, then review the redacted pages before you send the file. Redaction is a better fit than drawing a shape over the text, because the shape does not remove what lies beneath it.
Doing it in OmniDoc
- Download the desktop client from download.omnidoc.top and install it on Windows, macOS or Linux.
- Open your PDF in the PDF editor.
- If the file is a scan, run OCR and review the recognized text.
- Edit paragraph text in place, or add a signature or fill in form fields.
- Use redaction or page operations if the task needs them, then review each changed page.
- Export to Word, Excel or PowerPoint if you need an editable copy, or save the edited PDF under a new name.
❓ FAQ
1. Can I annotate a PDF without installing anything?
Yes. Online annotators run in a browser, but check their file size limits and privacy terms before you upload anything sensitive. Desktop readers and the OmniDoc desktop client need to be installed.
2. Which annotate PDF software works on Windows, macOS and Linux?
Some desktop PDF readers run on all three systems, so check each program's system requirements before you install one. The OmniDoc desktop client also runs on Windows, macOS and Linux. Pick the tool that matches the task: markup for a reader, edits and signatures for the editor.
3. Does editing a PDF change the original file?
Only the file you save changes. Before you start, save a copy of the untouched PDF, so you can compare the versions or return to the original if an edit goes wrong.
📝 Summary
To annotate a PDF with minimal cost, pick a reader for highlights and comments, and an editor for text changes, signatures and forms. Run OCR on scanned files first, and keep an original copy. Matching the tool to the job will save you time and reduce the risk of changing something you did not mean to change.
