How To Annotate PDF Online?
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Why does the Preview app make multiple copies of text annotations appear in a stack when I open a saved PDF?
This process is called merging of PDF files into one PDF file. You need to use a PDF editor for this or else u can choose online tools to merge it. For software you can use PDFelement or Online Pdf Annotator . For online you can use HiPDF or iLovePDF or PDFfiller. There are many other available over the internet for PDF editing.
Annotate PDF: All You Need to Know
And that's why you're looking for a PDF editor like OCR Reader from Phantom PDF. So don't worry, it is not too complicated for you, just follow the instructions carefully.