Love this one

With I ❤ PDF, besides converting a PDF files to another format, you can also convert any file to PDF. Just select an option form the thumbnails shown on the home page, and you can easily manage your PDF file easily. There are many functions such as Merging PDFs, Split PDFs, Rotate PDF, Unlock PDF and much much more...
You can even add page numbers to your existing document using the I ❤ PDF
OK, what if you don't have a working Internet when you need, yes you can't do it with I ❤ PDF, but no problem! this is where the sodaPDF comes in.

SodaPDF

The SodaPDF is a software which can work offline to edit your PDF files, You can download the free installer by visiting sodaPDF and can even use the online version. The site states that it is a reliable, intuitive and portable PDF software you can use at home and on the go.
By logging into the cloud service you can view the PDF files online, and you can also see your recently worked files and can also bookmark files you work the most with. You can compare PDF files by making them int o a two column view. Taking a snapshot of your document also is now easier with SodaPDF.

The Creator

With PDF-Creator you can convert every printable document to PDF and many other formats. You can create professional PDFs without paying a penny. You can easily download the installer and continue using it free from your PC too. The PDF-Creator supports 128-bit Advanced Encryption Standard(AES) encryption to secure your documents with a password.

PDF Printer

The DoPDF is a freeware that you can use to create PDF from any printable document. It's available for Windows only for now

A small one

The SmallPDF is can solve most of your problems while working with the PDFs. It's freely available to download and it's easy to convert and edit all your PDF files. Another good thing is that there is no file size limits, no ad watermarks - it's all free ...

Another few

The Uberflip is a Cloud-Based Content Experience Platform for Marketers, but you can use it to convert PDF files to eBooks using the flash player.

Using Paperjet, you can fill in a form online using PDF document, just upload a document you want to fill in. The paperjet will make the blank spaces fillable so you can start typing on it straight away. You can enter a URL of the document/form you need to fill or can use the "Drag & Drop" option. You can add a digital signature also in addition after you've done with editing.

Disclaimer:
All the sites listed above are from my knowledge only, and I have heard about some but won't them or I haven't even visited some of them. I am not reviewing or rating any of those, Just passing some information I know. These sites may not be permanent and may be changed or closed in future. I'm not responsible for any loss you can have using this websites, so use with caution, Thank you.