If you often create and edit PDF documents (whether ebooks, monographs, magazines, or reports), you know that tools for professional PDF editing are useful.
Some services and software are paid for. There are free services online, but they leave a watermark on the documents or white margins of a few millimeters, which is bad.
However, I know free and quality services (no watermarks, no limitations) that you can use, and the result is quality.
This is a well-known website with many free features for converting Word to PDF, merging multiple PDFs, optimizing and reducing file size, and converting PDF to PowerPoint.
Excel to PDF: edit a PDF file (add more text, images, annotations, etc.), protect and encrypt PDF files with a password, and much more.
Deft PDF
This is a similar free service. It has several PDF conversion options and also has a PDF document translation service.
Free translation allows translating small documents up to 5 pages; after that, they charge $1 per page.
Another free feature that I use is to merge PDF files into one, or merge JPG pages into one single PDF (to create a magazine, for example). It's free and unlimited.
These websites are multi-platform; they work in a web browser, on a tablet, or on a mobile phone. They have a mobile app.
Another excellent free service is PDF 2 GO.
I use it, for example, to resize a PDF file. For example, I have a PDF ebook that is 5x8 inches; I upload it and resize it to 6x9 inches.