How to comment on and annotate a PDF for review

If you are wondering how to annotate a PDF for someone else to review, the simple answer is: mark it up, save a copy and send that copy back. In our free PDF Studio, switch to Advanced and open the Comment tab. It has Highlight, Underline, Strike, Note, Draw and Box. Drag over the words you want to mark, click to add notes, then press Save PDF. Everything runs in your browser, so contracts, theses and reports never leave your device.

One thing to know before you start: PDF Studio makes your marks part of the page when you save. They look like comments, but they are not the "comment" objects some PDF readers list in a sidebar. Read the section on what that means before you choose this way of working.

What each Comment tool does

Tool	What it does	Good for
Highlight	A see-through colour block over text (yellow, green, blue or pink)	Key sentences, figures to check
Underline	A thin blue line under text	Wording to look at again
Strike	A thin red line through text	Words or numbers to delete
Note	A small yellow box you type in	Questions, corrections, explanations
Draw	Freehand ink with the mouse, a pen or your finger	Circles, arrows, quick sketches
Box	A rectangle outline	Framing a table, photo or paragraph

Highlight, Underline, Strike and Draw stay switched on after each use, so you can mark several places in a row. Press Esc, or choose Select, when you are done.

How to annotate a PDF in PDF Studio, step by step

1. Open the file. Go to PDF Studio and click Open PDF files, or drop the PDF onto the page.
2. Switch to Advanced. The tool starts in Simple mode, which has Highlight but not the full Comment tab. Tap More tools, or choose Advanced at the top of the Settings panel on the right.
3. Open the Comment tab. Its ribbon shows the six tools above.
4. Mark the text. Choose Highlight, Underline or Strike and drag along the words. To change a highlight's colour, pick another swatch under Highlight on the right before you drag, or select an existing highlight and change its colour and opacity.
5. Add notes. Choose Note and click next to the part you are commenting on. A yellow box appears with the word "Note"; type your comment over it. Change the font size on the right if it needs to be smaller or larger.
6. Circle or point. Use Draw for arrows and circles, or Box to frame an area. The line width is set on the right.
7. Fix mistakes. Choose Select, click a mark and press Delete, or use Ctrl+Z to undo.
8. Save and send. Press Save PDF (or Ctrl+S). The new file ends in -edited.pdf; rename it to something clear, such as agreement-review-ali.pdf, and send it back.

If you need to stop halfway, you can close the tab: PDF Studio keeps unfinished work in your browser for a week and offers to continue next time.

Real comments versus marks on the page

PDF files can hold two kinds of review marks:

• Comment objects sit on top of the page. Some PDF readers list them in a sidebar, show the author's name, and let people reply, hide or resolve them.
• Page marks are drawn into the page itself, like ink on paper. Every reader shows them the same way, on a phone, a computer or in print, but they can't be listed, replied to or switched off.

PDF Studio makes page marks. The Comment tab's own tip says so: highlights, lines, notes and drawings become part of the page when you save.

That is often an advantage. Your notes look the same in a phone's PDF viewer, in a computer's browser and on a printed copy, and nobody can accidentally hide them. It is less suited to long back-and-forth reviews where several people reply to each other's comments inside one file.

Working with several reviewers

Because saved marks can't be edited again, agree on a simple routine:

• Give each reviewer a different highlight colour, for example yellow for the first and blue for the second.
• Start each note with your initials, such as "RK: check this date".
• Pass the file along in order: the second reviewer opens the first reviewer's saved copy and adds to it.
• Keep the clean original, so the author can make changes in the real document and produce a fresh PDF.

Tips for clear review notes

• Be specific. "Change 15 to 30 days" is easier to act on than "Wrong?".
• Put the note in the margin. Notes placed over text hide it. Drag them to white space next to the line.
• Use Strike plus a Note for changes. Strike the old words, then write the new wording in a note beside them.
• Write in Bangla if that is easier. Text the standard PDF fonts can't show is saved as a sharp picture of the text, so Bangla notes look right in any reader.
• Check the last page. Reviewers often forget to mark appendices and attachments.

When the review is finished

Once everyone agrees, the author edits the original document, makes a new PDF, and the parties sign it. For signing, use the Fill & Sign tab in PDF Studio or the simpler Sign PDF. Contracts often ask for initials on every page too; see how to add initials to every page of a PDF contract.

If the marked-up file is too large to email, switch on compression before saving, or use Compress PDF afterwards.

Common problems and how to fix them

I only see Fill & Sign, Pages and Save

You are in Simple mode. Choose More tools or Advanced on the right to see the Comment tab.

My highlight hides the text

Select it and lower the opacity on the right, or pick a lighter colour.

I want to change a note after saving

You can't edit it in the saved file. If you still have the tab open, change the note and save again. Otherwise, open your original file and annotate it again.

Quick checklist

• Original file kept, unmarked
• Advanced mode on, Comment tab open
• One highlight colour per reviewer; notes start with initials
• Notes placed in the margin, not over text
• Saved copy renamed clearly and checked page by page
• Compressed if it must go by email