Convert PDF to Highlightable PDF: Marking Up a Scan

You cannot highlight text in a scanned PDF because its pages are pictures, with no words for the highlighter to hold on to. To convert a PDF to a highlightable PDF, run it through OCR and save a searchable copy. The words then become selectable, and a text highlight can follow them across the line.

Why will the highlighter not grab words in a scanned PDF?

The highlighter will not grab words in a scanned PDF because a text highlight is attached to stored characters, and a scan stores none. The tool looks for letters under the cursor, finds a picture, and either does nothing or drags out a rectangle as if you were cropping a photograph.

A text highlight is a note pinned to a run of characters. The program has to know where a word starts and ends before it can color it. Adobe's instructions for adding markups in Acrobat show the dependency in their order: the step "Use the Select text tool from Quick action toolbar to select the text" comes before the choice "To highlight a text, select Highlight text". Where no text can be selected, there is nothing for that second step to act on.

Once selection works, drag across a pleading caption, an affidavit jurat, and a contract clause. The color should cover the same line you see on the page image. If the file holds records, try a medical provider name the same way. Color that sits beside the letters, or that covers the whole line, means the words are stored and their positions are off.

Scans, faxes and photographed pages saved as PDF all behave this way. The post on why you cannot copy text from a PDF describes the file type under what an image-only PDF is.

A file can also be mixed. If the highlighter works on the cover letter and fails from page three onward, the later pages are pictures bound in behind typed ones.

Converting a PDF so its words can be selected and highlighted

Converting a PDF so its words can be selected and highlighted means adding a text layer with OCR and saving the result as a searchable PDF. The page pictures stay, and recognized characters are stored with them. Once the file holds characters, the select tool and the highlighter both have something to work with.

1. Copy the file. Mark up the copy. The scan as you received it stays clean.
2. Run OCR and save a searchable PDF. Any tool that writes a text layer into the PDF will do. In Schema Law you upload the PDF, PNG or JPEG and choose Searchable PDF from the exports, which the free plan includes for a document of up to three pages.
3. Test selection before you start marking. Open the new file, pick a page in the middle, and drag across one sentence. Watch what turns blue.
4. Test the highlighter on the same sentence. If the color covers the words you dragged across, the file is ready.
5. Name it as a working copy. A suffix such as _markup tells the next person this file carries your notes.

Step 3 is the one that matters, because "selectable" and "highlightable where you expect" are different results. A PDF converted to a selectable PDF lets you copy its text. Whether a highlight sits neatly on a phrase depends on how the tool positioned the hidden words. Schema Law's homepage describes its export as "Your original file with a hidden text layer, so search finds the page", which is a promise about search, not about marking individual words. Try your own export on a real page before planning a long markup session around it.

Convert first and mark up second. Notes made on the scan before conversion may or may not come through the OCR step, depending on the tool. The post on what a conversion keeps deals with that under comments, highlights and stamps on a PDF that goes through OCR.

Why does a highlight land beside the words or swallow the whole line?

A highlight lands beside the words or swallows the whole line when the hidden text is not positioned word for word under the print. The highlighter colors the place where the stored text says a word is. If the text was placed by line or by page, the color follows that placement and not the picture.

The mechanics of placement are explained in the post on searchable PDFs under how the hidden text is lined up with the picture.

You have three ways forward when placement is off:

• Accept it for reading copies. A highlight on the correct line still tells you where to look.
• Draw the mark by hand. A drawn box goes exactly where you put it and ignores the hidden text.
• Convert again with a different tool. If precise text highlights matter, for example in a transcript you will mark line by line, test tools on one page and keep the one whose highlights land on the words.

Drawing a highlight box on a scan versus highlighting real text

A drawn highlight box is a shape placed on the page by position. A real text highlight is a mark tied to particular characters. Both look like yellow over words. Only the second knows which words it covers, and that difference shows up when you search, summarize or reuse your markup.

Neither is the better tool in every case. On a page of handwriting, or over a seal, a drawn box is the only mark available. On forty pages of testimony where you will later pull every highlighted answer into an outline, text highlights are worth the conversion.

One caution applies to both. A colored box over words hides nothing and removes nothing, and it is not a redaction. If text has to be withheld, use a redaction tool and follow the sequence in the post on whether to run OCR before or after redaction.

Do highlights and notes stay with the PDF when you send it?

Highlights and notes are saved inside the PDF as annotations, so they travel with the file when you send it. The recipient sees them if their program displays annotations, and can read any note text you typed. Decide before sending whether your markup is meant for that reader.

That has two consequences.

Your notes go where the file goes. A highlight shows the reader which passages you marked. A sticky note reading "weak point, ask client" tells them more. Open the comments list in your PDF program and read every entry before a marked-up file leaves the office. Whether a given note is protected, and what happens if it is disclosed, is a question for the lawyer responsible for the matter.

The recipient can change them. Annotations sit on top of the page and can be moved, edited or deleted by anyone with a PDF editor. If the marks have to stay fixed, some programs offer to flatten them into the page. Flattening can also rebuild pages as pictures and drop the text layer, so test the flattened file for search, and see the post on a PDF that is no longer searchable if it fails.

A short routine before sending:

• Keep three files: the scan as received, the clean searchable copy, and your marked-up copy.
• Send the clean searchable copy unless the recipient is supposed to see your marks.
• If they are, read the comments list first and delete anything not meant for them.
• Open the file you are about to send in a second PDF program and confirm the marks appear where you put them, since viewers differ in how they draw annotations.
• Print one marked page if the recipient will work on paper. Whether comments print depends on the print settings in the program used.

The export formats section of the homepage lists the other formats available from the same upload if a marked-up PDF turns out to be the wrong vehicle, such as Word for a document you would sooner comment on in a word processor.