Searchable PDF

The creation of searchable PDF files is one of the main uses of OCR software. PDF files created from word processing programs are usually already text searchable, since they were created from a machine-editable text source, but other PDFs, such as those created from scanned documents, are not unless OCRd first. Once a PDF file is made searchable, users can enter text in their PDF reader's search bar and locate it without having to look through the whole document themselves.

In order for a PDF to be made text-searchable, the text it contains must be extracted and converted to machine-editable text � i.e. the file must must be OCRd. This text is then used to create an invisible layer of text, which is added to the PDF. The invisible layer of text lines up with the visible text, which is actually just an image of text, and since it is recognized by the computer as text, rather than an image, can effectively used to search the visible text in the document.

PDF's ability to contain this layer of text is unique, which is why when image files such as JPEGs or TIFFs are OCRd with the intention of making them searchable, they are converted to PDF files. It is very important that the OCR software used to create the searchable PDF be accurate, since if it is not, the invisible, searchable text overlay will not actually correspond to the visible text. Of course, it is important that the PDF being made text-searchable be a clean, clear document; otherwise, even the most accurate OCR will have a hard time recognizing its text.

Depending on how many PDFs you need to make searchable, you may be able to get away with using a free online OCR tool. In order to use these services, you upload the file you want to OCR, and it either emails you the searchable file or allows you to download it. These tools are slow, and don't allow for any customization. More serious users can evaluate proprietary software through the use of free trial versions, which is the only real way to know what you are purchasing.