Text in a PDF file is permanently embedded to each page where it can no longer be edited unless the text is in a PDF form field that hasn't been "flattened". So, unlike a word processing or simple text file such as a Word document or .TXT or .RTF file, the text in a PDF document can't be edited any longer and is meant to be read-only, but you can still use DocHub to cover up any existing text by using the Whiteout Tool which will let you frame a white box around and over it. Then, if you want to then add new text in its place or add other annotations, just select the tool on the Tool Bar and click on the whited out area to add new text on top of the whiteout.
It's not currently possible to remove existing text from a document without using the Whiteout tool to cover it up and put any annotation you'd like on top of the whiteout or using our Insert Image or Stamp Tool to cover the text entirely. You can learn more about the selection of PDF editing tools in DocHub in the article below:
What type of PDF edits can I make?
The Difference Between Embedded Text and an Image of Text on a PDF
If you are unable to highlight text in a document to copy or to highlight using our text Highlight Tool then it is most likely a scanned image of text on paper instead of a regular PDF with embedded, digital text where you are just looking at a scanned image of the document instead. If you were the one who scanned the document and still have the original paper(s), there are some scanners that offer OCR (optical character recognition) technology which will attempt decipher any text on paper and then embed the text into your PDF.
If you do have a scanned image that doesn't have highlightable text, and you don't have the original paper document to rescan it, I would recommend downloading it from DocHub as PDF using File menu > Download > PDF and then use a free online OCR app to try to create a PDF with embedded text and then re-upload that new file to DocHub. To find an app to use, you can Google the web for "scanned text online OCR app", and there will be several free ones at the top of the results. It would be best to choose one that has a PDF output such as http://www.free-online-ocr.com.
Since some digital scans have better resolution and readability than others, using OCR on your document may or may not convert all of the scanned text into the most accurate embedded text depending on several factors such as how legible the text is in the original, the style of font, and the DPI (resolution) of the scan, so if the text is not detected and converted correctly after using the first free OCR online app, you should try using another one to see if it has better results.
Once you have a PDF file where its text is actually embedded and selectable and no longer an image, you can then simply re-upload the document to DocHub.